Blog O-On

The Manufacturing Of Iso-Butane

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Dec 2008 08:00:00 +0000

Iso-butane [(CH3)3CH] can be isolated from the petroleum C4 fraction or from natural gas by extraction and distillation. There are two major uses of iso-butane. One is dehydrogenation to isobutylene followed by conversion of the isobutylene to the gasoline additive methyl t-butyl ether (MTBE). However, current environmental issues may ban this gasoline additive. Iso-butane is also oxidized to the hydroperoxide and then reacted with propylene to give propylene oxide and t-butyl alcohol. The t-butyl alcohol can be used as a gasoline additive, or dehydrate to iso-butylene.

The Manufacturing Of Paint

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Dec 2008 08:00:00 +0000

Liquid paint is a dispersion of a finely divided pigment in a liquid (the vehicle) composed of a resin or binder and a volatile solvent (Fig. 1). The pigment, although usually an inorganic substance, may also be a pure, insoluble organic dye known as a toner, or an organic dye precipitated on an inorganic carrier such as aluminum hydroxide, barium sulfate, or clay, thus constituting a lake.
The solid particles in the paint reflect many of the destructive light rays, and thus help to prolong the life of the paint. In general, pigments should be opaque to ensure good covering power and chemically inert to secure stability, hence long life.

The Manufacturing Of Soap

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Dec 2008 08:00:00 +0000

Soaps are the sodium or potassium salts of certain fatty acids obtained from the hydrolysis of triglycerides.

Fat + NaOH → glycerol + R–CO2 –Na+

Soap comprises the sodium or potassium salts of various fatty acids, but chiefly of oleic, stearic, palmitic, lauric, and myristic acids.

Manufacturing processes are both batch (in which the triglyceride is steam-hydrolyzed to the fatty acid without strong caustic, and then in a separate step it is converted into the sodium salt) or continuous.

The manufacture of soap (Fig. 1) involves continuous splitting (hydrolysis) and, after separation of the glycerin, neutralization of the fatty acids to soap. The procedure is to split, or hydrolyze, the fat, and then, after separation from the glycerol (glycerin) to neutralize the fatty acids with a caustic soda solution:

(C17H35COO)3C3H5 + 3H2O → 3C17H35COOH + C3H5(OH)5

C17H35COOH + NaOH → C17H35COONa + H2O

In continuous, countercurrent splitting, the fatty oil is deaerated under a vacuum to prevent darkening by oxidation during processing. It is charged at a controlled rate to the bottom of the hydrolyzing tower through a sparge ring (Fig. 2). The oil in the bottom contacting section rises because of its lower density and extracts the small amount of fatty material dissolved in the aqueous glycerol (glycerin) phase. At the same time, deaerated, demineralized water is fed to the top contacting section, where it extracts the glycerol dissolved in the fatty phase. After leaving the contacting sections, the two streams enter the reaction zone where they are brought to reaction temperature by the direct injection of high-pressure steam, and then the final phases of splitting occur. The fatty acids are discharged from the top of the splitter or hydrolyzer to a decanter, where the entrained water is separated or flashed off. The glycerol-water solution is then discharged from the bottom of an automatic interface controller to a settling tank.

The Manufacturing Of Zinc oxide (ZnO)

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Dec 2008 08:00:00 +0000

Zinc oxide (ZnO) is manufactured by oxidizing zinc vapor in burners in which the concentration of zinc vapor and the flow of air are controlled to produce the desired particle size and shape. The hot gases and particulate oxide or fume pass through tubular coolers, and then the zinc oxide is separated in a baghouse. The purity of the zinc oxide depends upon the source of the zinc vapor.

In the indirect process, zinc metal vapor for burning is produced in several ways, one of which involves horizontal retorts. Since the entire vapor is burned in a combustion chamber, the purity of the oxide depends on that of the zinc feed. Oxide of the highest purity requires special high-grade zinc, and less-pure products are made by blending in Prime Western and even scrap zinc. In the direct process, four or more firebrick furnaces having common walls are charged in cyclic fashion. Coal that is hot from the previous charge is first spread on the grate and, after ignition, a damp, well-blended mixture of zinc ore or zinc-containing material and coal is added. The bed is maintained in a reducing condition with carbon monoxide to produce zinc and lead, if present. Metal vapors are drawn into a chamber above the furnace, where combustion air oxidizes them to pigment. The hot pigmentgas stream enters a cooling duct common to the whole block and, in this way, the product becomes a uniform blend. Traveling-grate furnaces can also be employed. In this process, anthracite briquettes are fed to a depth of about 15 cm. After ignition by the previous charge, the coal briquettes are covered by ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and burns in a combustion chamber, and the spent clinker falls into containers for removal. A pigment-grade zinc oxide rotary kiln uses high temperature to produce pigment-quality zinc oxide and makes possible higher recovery than a grate furnace.
Other processes include an electrothermic process, an electric-arc vaporizer process, and the slag fuming process. Zinc oxide, as an amphoteric material, reacts with acids to form zinc salts and with strong alkali to form zincates. In the vulcanization of rubber, the chemical role of zinc oxide is complex and the free oxide is required, probably as an activator. Zinc oxide reacts with organic acids to produce zinc soaps and also reacts with carbon dioxide in moist air to form oxycarbonate. Acidic gases, e.g., hydrogen sulfide, sulfur dioxide, and chlorine, react with zinc oxide, and carbon monoxide or hydrogen reduce it to the metal. At high temperatures, zinc oxide replaces sodium oxide in silicate glasses. An important biochemical property of the oxide is its fungicidal/mildewstatic action. It is also soluble in body fluids and soils. Zinc oxide of high purity is required for pharmaceutical, photoconductive, and certain other uses, and is manufactured by the indirect process. Less-pure zinc oxide is manufactured by the direct process, by which impure zinc oxide is reduced to zinc vapor that is then burned.

The Manufacturing Of Sulfuric acid 2

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 11 Dec 2008 08:00:00 +0000

Sulfuric acid is produced from sulfur, oxygen and water via the contact process.

In the first step, sulfur is burned to produce sulfur dioxide.

(1) S(s) + O2(g) → SO2(g)

This is then oxidized to sulfur trioxide using oxygen in the presence of a vanadium(V) oxide catalyst.

(2) 2 SO2 + O2(g) → 2 SO3(g) (in presence of V2O5)

Finally the sulfur trioxide is treated with water (usually as 97-98% H2SO4 containing 2-3% water) to produce 98-99% sulfuric acid.

(3) SO3(g) + H2O(l) → H2SO4(l)

Note that directly dissolving SO3 in water is not practical due to the highly exothermic nature of the reaction, forming a corrosive mist instead of a liquid. Alternatively, SO3 can be absorbed into H2SO4 to produce oleum (H2S2O7), which may then be mixed with water to form sulfuric acid.

(3) H2SO4(l) + SO3 → H2S2O7(l)

Oleum is reacted with water to form concentrated H2SO4.

(4) H2S2O7(l) + H2O(l) → 2 H2SO4(l)

The Manufacturing Of Aspirin

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 11 Dec 2008 08:00:00 +0000

Aspirin (acetylsalicylic acid) is by far the most common type of analgesic, an important class of compounds that relieve pain, and it also lowers abnormally high body temperatures. Aspirin also finds use in reducing inflammation caused by rheumatic fever and rheumatoid arthritis. The manufacture of aspirin is based on the synthesis of salicylic acid from phenol. Reaction of carbon dioxide with sodium phenoxide is an electrophilic aromatic substitution on the ortho, para-directing phenoxy ring. The ortho isomer is steam distilled away from the para isomer. C6H5OH + CO2 → HOC6H4CO2H Salicylic acid reacts easily with acetic anhydride to give aspirin. HOC6H4CO2H + (CH3CO)2O → CH3OCOC6H4CO2H + CH3CO2H In this process, a 500-gallon glass-lined reactor is needed to heat the salicylic acid and acetic anhydride for 2 to 3 hours. The mixture is transferred to a crystallizing kettle and cooled to 3oC. Centrifuging and drying of the crystals yields the bulk aspirin. The excess solution is stored and the acetic acid is recovered to make more acetic anhydride. The irritation of the stomach lining caused by aspirin can be alleviated with the use of mild bases such as sodium bicarbonate, aluminum glycinate, sodium citrate, aluminum hydroxide, or magnesium trisilicate (a trademark for this type of aspirin is Bufferin®). Both phenacetin and the newer replacement acetaminophen are derivatives of p-aminophenol. Although these latter two are analgesics and antipyretics, the aniline-phenol derivatives show little if any anti-inflammatory activity. p-Aminophenol itself is toxic, but acylation of the amino group makes it a convenient drug. A trademark for acetaminophen is Tylenol®. Excedrin® is acetaminophen, aspirin, and caffeine. Acetaminophen is easily synthesized from phenol.

The Manufacturing Of Acetone

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 11 Dec 2008 08:00:00 +0000

Acetone (dimethyl ketone, 2-propanone, CH3COCH3, melting point: –94.6oC, boiling point: 56.3oC, density: 0.783) is the simplest ketone and is a colorless liquid that is miscible in all proportions with water, alcohol, or ether. There are two major processes for the production of acetone (2-propanone). The feedstock for these is either iso-propyl alcohol [(CH3)2CHOH] or cumene [iso-propyl benzene, C6H5CH(CH3)2]. In the last few years there has been a steady trend away from iso-propyl alcohol and toward cumene, but iso-propyl alcohol should continue as a precursor since manufacture of acetone from only cumene would require a balancing of the market with the coproduct phenol from this process. Acetone is made from iso-propyl alcohol by either dehydrogenation (preferred) or air oxidation. These are catalytic processes at 500oC and 40 to 50 psi. The acetone is purified by distillation, boiling point 56oC and the conversion per pass is 70 to 85 percent, with the overall yield being in excess of 90 percent.
CH3CH(OH)CH3 → CH3C(=O)CH3 + H2 .2CH3CH(OH)
CH3 + O2 → CH3C(=O)CH3 + 2H2O
Cumene is also used as a feedstock for the production of acetone. In this process, cumene first is oxidized to cumene hydroperoxide followed by the decomposition of the cumene hydroperoxide into acetone and phenol. The hydroperoxide is made by reaction of cumene with oxygen at 110 to 115oC until 20 to 25 percent of the hydroperoxide is formed. Concentration of the hydroperoxide to 80% is followed by catalyzed rearrangement under moderate pressure at 70 to 100oC. During the reaction, the palladium chloride (PdCl2) catalyst is reduced to elemental palladium to produce hydrogen chloride that catalyzes the rearrangement, and reoxidation of the palladium is brought about by use of cupric chloride (CuCl2) that is converted to cuprous chloride (CuCl). The cuprous chloride is reoxidized during the catalyst regeneration cycle.The overall yield is 90 to 92 percent. By-products are acetophenone, 2-phenylpropan-2-ol, and α-methylstyrene. Acetone is distilled first at boiling point 56oC.
Vacuum distillation recovers the unreacted cumene and yields α−methylstyrene, which can be hydrogenated back to cumene and recycled. Further distillation separates phenol, boiling point 181oC, and acetophenone, boiling point 202oC.
In older industrial processes, acetone is prepared (1) by passing the vapors of acetic acid over heated lime. Calcium acetate is produced in the first step followed by a breakdown of the acetate into acetone and calcium carbonate:
CH3CO2H + CaO → (CH3CO2)2Ca + H2O (CH3CO2)2
Ca → CH3COCH3 + CaCO3
and (2) by fermentation of starches, such as maize, which produce acetone along with butyl alcohol. Acetone is a very important solvent and is widely used in the manufacture of plastics and lacquers. For storage purposes, acetone may be used as a solvent for acetylene. Acetone is the starting ingredient or intermediate for numerous organic syntheses. Closely related, industrially important compounds are diacetone alcohol [CH3COCH2COH(CH3)2], which is used as a solvent for cellulose acetate and nitrocellulose, as well as for various resins and gums, and as a thinner for lacquers and inking materials. Acetone is used for the production of methyl methacrylate, solvents, bisphenol A, aldol chemicals, and pharmaceuticals. Methyl methacrylate is manufactured and then polymerized to poly(methyl methacrylate), an important plastic known for its clarity and used as a glass substitute.
Aldol chemicals refer to a variety of substances desired from acetone involving an aldol condensation in a portion of their synthesis. The most important of these chemicals is methyl iso-butyl ketone (MIBK), a common solvent for many plastics, pesticides, adhesives, and pharmaceuticals. Bisphenol A is manufactured by a reaction between phenol and acetone, the two products from the cumene hydroperoxide rearrangement. Bisphenol A is an important diol monomer used in the synthesis of polycarbonates and epoxy resins. A product known as synthetic methyl acetone is prepared by mixing acetone (50%), methyl acetate (30%), and methyl alcohol (20%) and is used widely for coagulating latex and in paint removers and lacquers.

The Manufacturing Of Sulfuric Acid 1

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Mon, 24 Nov 2008 08:00:00 +0000

Sulfuric acid (oil of vitriol, H2SO4) is a colorless, oily liquid, dense, highly reactive, and miscible with water in all proportions. Heat is evolved when concentrated sulfuric acid is mixed with water and, as a safety precaution, the acid should be poured into the water rather than water poured into the acid. Anhydrous, 100% sulfuric acid, is a colorless, odorless, heavy, oily liquid (boiling point: 338oC with decomposition to 98.3% sulfuric acid and sulfur trioxide). Oleum is excess sulfur trioxide dissolved in sulfuric acid. For example, 20% oleum is a 20% sulfur trioxide–80% sulfuric acid mix. Sulfuric acid will dissolve most metals and the concentrated acid oxidizes, dehydrates, or sulfonates most organic compounds, sometimes causing charring.

The manufacture of sulfuric acid by the lead chamber process involves oxidation of sulfur to sulfur dioxide by oxygen, further oxidation of sulfur dioxide to sulfur trioxide with nitrogen dioxide, and, finally, hydrolysis of sulfur trioxide.

S + O2 → SO2

2NO +O2 → 2NO2

SO2+NO2 → SO3+NO

SO3 + H2O → H2SO4

Modifications of the process include towers to recover excess nitrogen oxides and to increase the final acid concentration from 65% (chamber acid) to 78% (tower acid).

The contact process has evolved to become the method of choice for sulfuric acid manufacture because of the ability of the process to produce stronger acid.

S + O2 → SO2

2SO2 +O2 → 2SO3

SO3 + H2O → H2SO4

In the process (Fig. 1), sulfur and oxygen are converted to sulfur dioxide at 1000oC and then cooled to 420oC. The sulfur dioxide and oxygen

enter the converter, which contains a catalyst such as vanadium pentoxide (V2O5). About 60 to 65% of the sulfur dioxide is converted by an exothermic reaction to sulfur trioxide in the first layer with a 2 to 4-second contact time. The gas leaves the converter at 600oC and is cooled to 400oC before it enters the second layer of catalyst. After the third layer, about 95% of the sulfur dioxide is converted into sulfur trioxide. The mixture is then fed to the initial absorption tower, where the sulfur trioxide is hydrated to sulfuric acid after which the gas mixture is reheated to 420oC and enters the fourth layer of catalyst that gives overall a 99.7% conversion of sulfur dioxide to sulfur trioxide. It is cooled and then fed to the final absorption tower and hydrated to sulfuric acid. The final sulfuric acid concentration is 98 to 99% (1 to 2% water). A small amount of this acid is recycled by adding some water and recirculating into the towers to pick up more sulfur trioxide.

Although sulfur is the common starting raw material, other sources of sulfur dioxide can be used, including iron, copper, lead, nickel, and zinc sulfides. Hydrogen sulfide, a by-product of petroleum refining and natural gas refining, can be burned to sulfur dioxide. Gypsum (CaSO4) can also be used but needs high temperatures to be converted to sulfur dioxide. Other uses for sulfuric acid include the manufacture of fertilizers, chemicals, inorganic pigments, petroleum refining, etching, as a catalyst in alkylation processes, in electroplating baths, for pickling and other operations in iron and steel production, in rayon and film manufacture, in the making of explosives, and in nonferrous metallurgy

Fatty alcohol

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Mon, 24 Nov 2008 08:00:00 +0000

Fatty alcohols are aliphatic alcohols derived from natural fats and oils, originating in plants, but also synthesized in animals and algae. Their significance in nutrition and health has historically been overlooked, and is only now being realized, as they are closely related to fatty acids, including the well-documented omega 3 fatty acids. The other counterparts are fatty aldehydes. Fatty alcohols usually have even number of carbon atoms. Production from fatty acids yields normal-chain alcohols—the alcohol group (-OH) attaches to the terminal carbon. Other processing can yield iso-alcohols—where the alcohol attaches to a carbon in the interior of the carbon chain.

Current and future uses
The smaller molecules are used in cosmetics and food, and as industrial solvents. Some of the larger molecules are simply seen as biofuels, but little research has been done until 2006 regarding many of these, and they have been shown to be have anticancer, antiviral, antifungal, anti-HIV properties, for potential use in medicine and health supplements.

Due to their amphipathic nature, fatty alcohols behave as nonionic surfactants. They find use as emulsifiers, emollients and thickeners in cosmetics and food industry.

Fatty alcohols are a common component of waxes, mostly as esters with fatty acids but also as alcohols themselves.

Nutrition
Very long chain fatty alcohols (VLCFA), obtained from plant waxes and beeswax have been reported to lower plasma cholesterol in humans. They can be found in unrefined cereal grains, beeswax, and many plant-derived foods. Reports suggest that 5–20 mg per day of mixed C24–C34 alcohols, including octacosanol and triacontanol, lower low-density lipoprotein (LDL) cholesterol by 21%–29% and raise high-density lipoprotein cholesterol by 8%–15%. Wax esters are hydrolyzed by a bile salt–dependent pancreatic carboxyl esterase, releasing long chain alcohols and fatty acids that are absorbed in the gastrointestinal tract. Studies of fatty alcohol metabolism in fibroblasts suggest that very long chain fatty alcohols, fatty aldehydes, and fatty acids are reversibly inter-converted in a fatty alcohol cycle. The metabolism of these compounds is impaired in several inherited human peroxisomal disorders, including adrenoleukodystrophy and Sjögren-Larsson syndrome. Concentrations of VLCFA in blood plasma increase during fasting and when children are placed a ketogenic diet to suppress seizures.

Winemaking considerations

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Mon, 24 Nov 2008 08:00:00 +0000

During fermentation there are several factors that winemakers take into consideration. The most notable is that of the internal temperature of the must. The biochemical process of fermentation itself creates a lot of residual heat which can take the must out of the ideal temperature range for the wine. Typically white wine is fermented between 64-68 °F (18-20 °C) though a wine maker may choose to use a higher temperature to bring out some of the complexity of the wine. Red wine is typically fermented at higher temperatures up to 85 °F (29 °C). Fermentation at higher temperatures may have adverse effect on the wine in stunning the yeast to inactivity and even "boiling off" some of the flavors of the wines. Some winemakers may ferment their red wines at cooler temperatures more typical of white wines in order to bring out more fruit flavors

To control the heat generated during fermentation the winemaker has to choose a suitable vessel size or to use cooling devices of various sorts from the ancient Bordeaux traditions of placing the fermentation vat on top of blocks of ice to today's modern use of sophisticated fermentation tanks with built in cooling rings.

A risk factor involved with fermentation is the development of chemical residue and spoilage which can be corrected with the addition of sulfur dioxide (SO2), although excess SO2 can lead to a wine fault. A winemaker who wishes to make a wine with high levels of residual sugar (like a dessert wine) may stop fermentation early either by dropping the temperature of the must to stun the yeast or by adding a high level of alcohol (like brandy) to the must to kill off the yeast and create a fortified wine.

Uses of Sulfuric acid

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Tue, 11 Nov 2008 08:00:00 +0000

Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acid production is a good indicator of its industrial strength. The major use (60% of total production worldwide) for sulfuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers as well as trisodium phosphate for detergents. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as:

Ca5F(PO4)3 + 5 H2SO4 + 10 H2O → 5 CaSO4•2 H2O + HF + 3 H3PO4.

Sulfuric acid is used in large quantities by the iron and steelmaking industry to remove oxidation, rust and scale from rolled sheet and billets prior to sale to the automobile and white-goods industry. Used acid is often recycled using a Spent Acid Regeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide (SO2) and sulfur trioxide (SO3) which are then used to manufacture "new" sulfuric acid. SAR plants are common additions to metal smelting plants, oil refineries, and other industries where sulfuric acid is consumed in bulk, as operating a SAR plant is much cheaper than the recurring costs of spent acid disposal and new acid purchases.

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.

Another important use for sulfuric acid is for the manufacture of aluminum sulfate, also known as paper maker's alum. This can react with small amounts of soap on paper pulp fibers to give gelatinous aluminum carboxylates, which help to coagulate the pulp fibers into a hard paper surface. It is also used for making aluminum hydroxide, which is used at water treatment plants to filter out impurities, as well as to improve the taste of the water. Aluminum sulfate is made by reacting bauxite with sulfuric acid:

Al2O3 + 3 H2SO4 → Al2(SO4)3 + 3 H2O.

Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanoneoxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much H2SO4 is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also important in the manufacture of dyestuffs solutions and is the "acid" in lead-acid (car) batteries.

Sulfuric acid is also used as a general dehydrating agent in its concentrated form. See Reaction with water.

Sulfur-iodine cycle

The sulfur-iodine cycle is a series of thermo-chemical processes used to obtain hydrogen. It consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen.

2 H2SO4 → 2 SO2 + 2 H2O + O2 (830°C)
I2 + SO2 + 2 H2O → 2 HI + H2SO4 (120°C)
2 HI → I2 + H2 (320°C)

The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This process is endothermic and must occur at high temperatures, so energy in the form of heat has to be supplied.

The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy. It does not require hydrocarbons like current methods of steam reforming.

The sulfur-iodine cycle is currently being researched as a feasible method of obtaining hydrogen, but the concentrated, corrosive acid at high temperatures poses currently insurmountable safety hazards if the process were built on large-scale.

Sulfuric acid

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Tue, 11 Nov 2008 08:00:00 +0000

Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include ore processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis.

Many proteins are made of sulfur-containing amino acids (such as cysteine and methionine) which produce sulfuric acid when metabolized by the body.
Contents

Occurrence

Pure (undiluted) sulfuric acid is not encountered on Earth, due to sulfuric acid's great affinity for water. Apart from that, sulfuric acid is a constituent of acid rain, which is formed by atmospheric oxidation of sulfur dioxide in the presence of water - i.e., oxidation of sulfurous acid. Sulfur dioxide is the main byproduct produced when sulfur-containing fuels such as coal or oil are burned.

Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as iron sulfide. The resulting water can be highly acidic and is called Acid Mine Drainage (AMD). This acidic water is capable of dissolving metals present in sulfide ores, which results in brightly-colored, toxic streams. The oxidation of iron sulfide pyrite by molecular oxygen produces iron(II), or Fe2+:

2 FeS2 + 7 O2 + 2 H2O → 2 Fe2+ + 4 SO42− + 4 H+.

The Fe2+ can be further oxidized to Fe3+, according to:

4 Fe2+ + O2 + 4 H+ → 4 Fe3+ + 2 H2O,

and the Fe3+ produced can be precipitated as the hydroxide or hydrous oxide. The equation for the formation of the hydroxide is

Fe3+ + 3 H2O → Fe(OH)3 + 3 H+.

The iron(III) ion ("ferric iron", in casual nomenclature) can also oxidize pyrite. When iron(III) oxidation of pyrite occurs, the process can become rapid. pH values below zero have been measured in ARD produced by this process.

ARD can also produce sulfuric acid at a slower rate, so that the Acid Neutralization Capacity (ANC) of the aquifer can neutralize the produced acid. In such cases, the Total Dissolved solids (TDS) concentration of the water can be increased form the dissolution of minerals from the acid-neutralization reaction with the minerals.

[edit] Extraterrestrial sulfuric acid

[edit] The cycle, in atmosphere of Venus

Sulfuric acid is produced in the upper atmosphere of Venus by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapor. Ultraviolet photons of wavelengths less than 169 nm can photodissociate carbon dioxide into carbon monoxide and atomic oxygen.
Atomic oxygen is highly reactive. When it reacts with sulfur dioxide, a trace component of the Venusian atmosphere, the result is sulfur trioxide, which can combine with water vapor, another trace component of Venus's atmosphere, to yield sulfuric acid.

CO2 → CO + O
SO2 + O → SO3
SO3 + H2O → H2SO4

In the upper, cooler portions of Venus's atmosphere, sulfuric acid exists as a liquid, and thick sulfuric acid clouds completely obscure the planet's surface when viewed from above. The main cloud layer extends from 45–70 km above the planet's surface, with thinner hazes extending as low as 30 and as high as 90 km above the surface.

The permanent venusian clouds produce a concentrated acid rain, as the clouds on the atmosphere of Earth produce water rains.
Thus, it's exist a double combined cycle of sulfur dioxide and water, because when sulfuric drops fall down, they are heated up and release water vapor, becoming more and more concentrated. And when they reach above 300°C, sulfuric acid begins to decompose in sulfur trioxide and water (both gaseous). sulfur trioxide is highly reactive (like sulfuric acid) and become sulfuric dioxide and oxygen, which oxides traces of CO, or surface rocks.
Sulfuric dioxide and water (vapor) continuously equilibrate their pressure from deep venusian atmosphere to upper altitudes, where they will be transformed again in sulfuric acid, and the cycle is closed !

[edit] On Europa's icy surface

Infrared spectra from NASA's Galileo mission show distinct absorptions on Jupiter's moon Europa that have been attributed to one or more sulfuric acid hydrates. The interpretation of the spectra is somewhat controversial. Some planetary scientists prefer to assign the spectral features to the sulfate ion, perhaps as part of one or more minerals on Europa's surface.

Ester reactions

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Fri, 24 Oct 2008 08:00:00 +0000

Esters react in a number of ways:

* Esters may undergo hydrolysis - the breakdown of an ester by water. This process can be catalyzed both by acids and bases. The base-catalyzed process is called saponification. The hydrolysis yields an alcohol and a carboxylic acid or its carboxylate salt.
* Esters also react if heated with primary or secondary amines, producing amides.
* Phenyl esters react to hydroxyarylketones in the Fries rearrangement.
* Di-esters such as diethyl malonate react as nucleophile with alkyl halides in the malonic ester synthesis after deprotonation.
* Specific esters are functionalized with an α-hydroxyl group in the Chan rearrangement.
* Esters are converted to isocyanates through intermediate hydroxamic acids in the Lossen rearrangement.
* Esters with β-hydrogen atoms can be converted to alkenes in ester pyrolysis.

Ester

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Fri, 24 Oct 2008 08:00:00 +0000

Esters are a class of chemical compounds and functional groups. Esters consist of an inorganic or organic acid in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group. Some acids that are commonly esterified are carboxylic acids, phosphoric acid, sulfuric acid, nitric acid, and boric acid. Volatile esters, particularly carboxylate esters, often have a pleasant smell and are found in perfumes, essential oils, and pheromones, and give many fruits their scent. Ethyl acetate and methyl acetate are important solvents; fatty acid esters form fat and lipids; phosphoesters form the backbone of DNA molecules; nitrate esters are known for their explosive properties (best known: nitroglycerin) and polyesters are important plastics. Cyclic esters are called lactones. The name "ester" is derived from the German Essig-Äther (literally: vinegar ether), an old name for ethyl acetate. Esters can be synthesized in a condensation reaction between an acid and an alcohol in a reaction known as esterification.

Dehydrogenation

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Fri, 24 Oct 2008 08:00:00 +0000

Dehydrogenation is a chemical reaction that involves the elimination of hydrogen (H2). It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures.

There are a variety of classes of dehydrogenations:

* Aromatization - Six-membered alicyclic rings can be aromatized in the presence of hydrogenation catalysts, the elements sulfur and selenium, or quinones (such as DDQ).
* Oxidation - The conversion of alcohols to ketones or aldehydes can be effected by metal catalysts such as copper chromite. In the Oppenauer oxidation, hydrogen is transferred from one alcohol to another to bring about the oxidation.
* Dehydrogenation of amines - amines can be converted to nitriles using a variety of reagents, such as IF5.
* Dehydrogenation of paraffins and olefins - paraffins like n-pentane and isopentane can be converted to pentene and isoprene.

Dehydrogenation converts saturated fats to unsaturated fats.

Enzymes that catalyze dehydrogenation are called dehydrogenases.

Equipment for crystallization

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Sep 2008 08:00:00 +0000

1. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquid is drained and the crystals removed. Nucleation and size of crystals are difficult to control. Typically, labor costs are very high.

2. Scraped surface crystallizers. One type of scraped surface crystallizer is the Swenson-Walker crystallizer, which consists of an open trough 0.6m wide with a semicircular bottom having a cooling jacket outside. A slow-speed spiral agitator rotates and suspends the growing crystals on turning. The blades pass close to the wall and break off any deposits of crystals on the cooled wall. The product generally has a somewhat wide crystal-size distribution.

3. Double-pipe scraped surface crystallizer. Also called a votator, this type of crystallizer is used in crystallizing ice cream and plasticizing margarine. Cooling water passes in the annular space. An internal agitator is fitted with spring-loaded scrapers that wipe the wall and provide good heat-transfer coefficients.

4. Circulating-liquid evaporator-crystallizer. Also called Oslo crystallizer. Here supersaturation is reached by evaporation. The circulating liquid is drawn by the screw pump down inside the tube side of the condensing stream heater. The heated liquid then flows into the vapor space, where flash evaporation occurs, giving some supersaturation.The vapor leaving is condensed. The supersaturated liquid flows down the downflow tube and then up through the bed of fluidized and agitated crystals, which are growing in size. The leaving saturated liquid then goes back as a recycle stream to the heater, where it is joined by the entering fluid. The larger crystals settle out and slurry of crystals and mother liquid is withdrawn as a product.

5. Circulating-magma vacuum crystallizer. The magma or suspension of crystals is circulated out of the main body through a circulating pipe by a screw pump. The magma flows though a heater, where its temperature is raised 2-6 K. The heated liquor then mixes with body slurry and boiling occurs at the liquid surface. This causes supersaturation in the swirling liquid near the surface, which deposits in the swirling suspended crystals until they leave again via the circulating pipe. The vapors leave through the top. A steam-jet ejector provides vacuum.

6. Continuous oscillatory baffled crystallizer (COBCTM). The COBCTM is a tubular baffled crystallizer that offers plug flow under laminar flow conditions (low flow rates) with superior heat transfer coefficient, allowing controlled cooling profiles, e.g. linear, parobolic, discontinued, step-wise or any type, to be achieved. This gives much better control over crystal size, morphology and consistent crystal products. For further information see oscillatory baffled reactor.

Crystal production

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Wed, 24 Sep 2008 08:00:00 +0000

From a material industry perspective:

* Macroscopic crystal production, for supply the demand of natural-like crystals with methods that "accelerate time-scale" for massive production and/or perfection:
o ionic crystal production;
o covalent crystal production.
* Tiny size crystals:
o Powder, sand and smaller sizes: using methods for powder and controlled (nanotechnology fruits) forms.
+ Mass-production: on chemical industry, like salt-powder production.
+ Sample production: small production of tiny crystals for material characterization. Controlled recrystallization is an important method to supply unusual crystals, that are needed to reveal the molecular structure and nuclear forces inside a typical molecule of a crystal. Many techniques, like X-ray crystallography and NMR spectroscopy, are widely used in chemistry and biochemistry to determine the structures of an immense variety of molecules, including inorganic compounds and bio-macromolecules.
o Thin film production.

Massive production examples:

* "Powder salt for food" industry;
* Silicon crystal wafer production.
* Production of sucrose from sugar beet, where the sucrose is crystallized out from an aqueous solution.

Ethyl acetate Uses

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 11 Sep 2008 08:00:00 +0000

• Solvent

Ethyl acetate is primarily used as a solvent. For example, it is commonly used to clean circuit boards to wash away any remaining flux residue, to dissolve the pigments for nail varnishes, and is responsible for the solvent-effect of some nail varnish remover (acetone and acetonitrile are also used). Industrially it is used to decaffeinate coffee beans and tea leaves. It is also used in paints as an activator or hardener.

In the laboratory, mixtures of ethyl acetate and other solvents are commonly used in chromatography. It is also used as a solvent for extractions. Ethyl acetate is rarely selected as a reaction solvent because it is prone to hydrolysis.

Like most simple esters, ethyl acetate has a fruity smell. Ethyl acetate is present in confectionery, perfumes, and fruits. In perfumes, it evaporates quickly, leaving but the scent of the perfume on the skin.

• Occurrence in wines
Ethyl acetate is the most common ester found in wine, being the product of the most common volatile organic acid-acetic acid and the ethanol alcohol created during the fermentation of wine. The aroma of ethyl acetate is most vivid in younger wines and contribute towards the general perception of "fruitiness" in the wine. Sensitivity varies with most people having a perception threshold around 120 mg/l. Excessive amounts of ethyl acetate is considered a wine fault. Exposure to oxygen can exacerbate the fault due to the oxidation of ethanol creating acetaldehyde. This can leave the wine with a sharp vinegar like taste.

• Other uses
In the field of entomology, ethyl acetate is an effective poison for use in insect collecting and study. In a killing jar charged with ethyl acetate, the vapors will kill the collected (usually adult) insect quickly without destroying it. Because it is not hygroscopic, ethyl acetate also keeps the insect soft enough to allow proper mounting suitable for a collection.

Industrial production of Ethyl acetate

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 11 Sep 2008 08:00:00 +0000

Industrially, ethyl acetate can be produced by the catalytic dehydrogenation of ethanol. For cost reasons, this method is primarily applied to conversion of surplus ethanol feedstock as opposed to predetermined generation on an industrial scale. In addition, it is commonly accepted as far less practical and less cost effective.

Catalysts for dehydrogenation include copper, operating at an elevated temperature but below 250 °C. The copper may have its surface area increased by depositing it on zinc, promoting the growth of snowflake, fractal like, structures. This surface area can be again increased by deposition onto a zeolite, typically ZSM-5. Traces of rare earth metals or alkalies, such as that of sodium and potassium, have also been found to be beneficial to the process. Byproducts of hydrogenation include diethyl ether (thought to primarily arise due to aluminum sites in the catalyst), acetaldehyde, acetaldehyde aldol products, higher esters and ketones. Acetaldehyde and MEK complicate conversion and purification as ethanol forms an azeotrope with water, as does ethyl acetate with ethanol and water and MEK with both ethanol and the acetate. To obtain a high purity product, these azeotropes must be "broken", and this can be achieved by making use of pressure swing distillation.

The composition of the distillate removed from the conversion products is biased towards acetate at atmospheric pressure and ethanol at increased pressure. First, the raw product is fed into a high pressure column where the bulk of the contaminating ethanol is removed. By then feeding the ethanol depleted distillate into a low pressure column, the acetate can be removed from the remaining ethanol azeotrope.

MEK forms during the conversion process from 2-butanol. The latter fails to form an azeotrope with the acetate and so MEK can be removed by hydrogenation of the contaminated product over nickel and further distillation to strip away 2-butanol. This provides the simultaneous benefit of removing the acetylaldehyde contaminant by returning it to an ethanol form and is easily accomplished as hydrogen is a byproduct of the initial dehydrogenation process.

It may also be possible to break the azeotropes with the use of membrane distillation, molecular sieves, an entrainer or absorption medium.

The distilled ethanol and rehydrogenated contaminants can then be recycled into the raw feedstock.

Thermodynamic view of crystallization

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Sun, 24 Aug 2008 08:00:00 +0000

The nature of a crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have a major impact on the size, number, and shape of crystals produced.

Now put yourself in the place of a molecule within a pure and perfect crystal, being heated by an external source. At some sharply defined temperature, a bell rings, you must leave your neighbours, and the complicated architecture of the crystal collapses to that of a liquid. Textbook thermodynamics says that melting occurs because the entropy, S, gain in your system by spatial randomization of the molecules has overcome the enthalpy, H, loss due to breaking the crystal packing forces:

T(S{liquid} - S{solid}) > H{liquid} - H{solid}

G{liquid} <>

Purification of Crystallization

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Sun, 24 Aug 2008 08:00:00 +0000

Well formed crystals are expected to be pure because each molecule or ion must fit perfectly into the lattice as it leaves the solution. Impurities would normally not fit as well in the lattice, and thus remain in solution preferentially. Hence, molecular recognition is the principle of purification in crystallization. However, there are instances when impurities incorporate into the lattice, hence, decreasing the level of purity of the final crystal product. Also, in some cases, the solvent may incorporate into the lattice forming a solvate. In addition, the solvent may be 'trapped' (in liquid state) within the crystal formed, and this phenomenon is known as inclusion.

Crystallization

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Sun, 24 Aug 2008 08:00:00 +0000

Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from an identical solution or melt, or more rarely deposited directly from a gas. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

The crystallization process consists of two major events, nucleation and crystal growth. Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that becomes stable under the current operating conditions. These stable clusters constitute the nuclei. However when the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.

The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Nucleation and growth continue to occur simultaneously while the supersaturation exists. Supersaturation is the driving force of the crystallization, hence the rate of nucleation and growth is driven by the existing supersaturation in the solution. Depending upon the conditions, either nucleation or growth may be predominant over the other, and as a result, crystals with different sizes and shapes are obtained (control of crystal size and shape constitutes one of the main challenges in industrial manufacturing, such as for pharmaceuticals). Once the supersaturation is exhausted, the solid-liquid system reaches equilibrium and the crystallization is complete, unless the operating conditions are modified from equilibrium so as to supersaturate the solution again.

Many compounds have the ability to crystallize with different crystal structures, a phenomenon called polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products.

There are many examples of natural process that involve crystallization.

Geological time scale process examples include:

* Natural (mineral) crystal formation (see also gemstone);
* Stalactite/stalagmite, rings formation.

Usual time scale process examples include:

* Snow flakes formation (see also Koch snowflake);
* Honey crystallization (nearly all types of honey crystallize).

Basic Steps in the Production of Ethyl Alcohol (part 2)

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 24 Jul 2008 08:00:00 +0000

CONVERSION WITH BARLEY MALT

Instead of using commercial enzymes, it is possible to affect conversion by employing barley malt -- at the ratio of 15% by weight, or 7 pounds per bushel -- in both the pre- and post-boil. However, such a technique requires a more acidic medium (about pH 4-5) and lower temperatures -- about 145 deg F (63 deg C) is optimum -- than MOTHER's powders. Though the weights and temperatures differ, the same sequence is followed as discussed in "Conversion With MOTHER's Enzymes".

(One way to speed up the cooking process is with steam, which -- at 350 deg F, 177 deg C -- reduces the cooking time to one minute. Another commercial approach is to use extruders: machines much like meat grinders that compress, grind, and convert the grain in a one-step process.)
FERMENTATION

If you use barley malt for the conversion process -- or if you are following some alternative recipe that does not employ MOTHER's Fermentation Powder -- you will need to add your own yeast.

Mix up two ounces of distiller's or baker's yeast in a quart or two of the liquid mash, and add the concoction to the wort. Vigorous agitation will oxygenate the mixture and encourage a rapid initial growth of the yeast culture.

Yeast plants can propagate in a solution with or without air, so agitate only enough to saturate the wort with air and then let it stand still. If the mash is continually agitated, the yeast will reproduce faster and make less waste: carbon dioxide and alcohol. But if the solution becomes anaerobic (without air) the yeast slows down reproduction and makes more alcohol and carbon dioxide.

Yeast also produces enzymes of its own to convert complex sugars. Since sugar conversion and alcohol conversion can take place simultaneously, the amylase enzymes and the yeast work in cooperation to convert the dextrins to glucose and fructose and then to alcohol and C02.

Fermentation is a chemical process and produces heat. In concentrated or particularly large mashes, the temperature can actually rise to levels dangerous to yeast. Since the ideal temperature for yeast is around 85 deg F, it's best to maintain that temperature by either utilizing cooling coils or keeping the water-to-grain ratio at about 40 gallons per bushel.

Conversion of sugars to alcohol and C02 will be completed in three to five days, depending on the temperature of the mixture and the type of yeast used. You can tell when the mash is done by watching the "cap" of solids on top of the solution. During fermentation, the rising C02 keeps the solids in constant motion, but when the bubbling stops, the solids fall to the bottom. At this time, you're ready to separate the solids from the liquids and begin distillation.
KEEP IT CLEAN!

Remember, sanitation is extremely important! There are many kinds of invading bacteria, including strains which can withstand boiling temperatures. So, observe the same standards that any restaurant or kitchen follows. And keep the fermenting vat well covered: a fly in the ointment will turn your mash into something that it's best to keep upwind of.

Basic Steps in the Production of Ethyl Alcohol (part 1)

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Thu, 24 Jul 2008 08:00:00 +0000

THE usual sources of raw material for alcohol production from starch are cereal grains such as corn, wheat, rye, barley, milo (sorghum grains), rice, etc. Other types of starch are available from potatoes of all kinds, Jerusalem artichokes, and other high-starch vegetables. Starch conversion is the standard method of production and the one we will discuss here.

It is possible, however, to make alcohol from sugar-producing plants (saccharine material) such as sugar beets, sugarcane, fruits, and others. These substances need no milling (as do grains), but they do require some kind of grinding or squeezing process. Rapid, efficient fermentation of these sugars has not been as well explored as the process using starch.

A third source of fermentables is cellulose, as found in wood and waste sulphite liquor. This more complex process requires the use of acids to reduce the material to wood sugars. Consequently, most do-it-yourselfers should stick to either starch or sugar.

MILLING

All grains must be ground before mashing to expose the starch granules and help them remain in suspension in a water solution. The grain should be ground into a meal -- not a flour! -- that will pass a 20-mesh screen. On a hammermill, however, a 3/16" screen will suffice.

Potatoes and similar high-moisture starch crops should be sliced or finely chopped. Since potato starch granules are large and easily ruptured, it isn't necessary to maintain the hard rapid boil which is required of the tougher, dryer "flinty" starches found in grains.

CONVERSION WITH MOTHER'S ENZYMES

For small batches (5 bushels or less), fill the cooker with water (30 gallons per bushel), and add the meal slowly, to prevent lumps from forming. (When, cooking with steam, or at higher temperatures, it is possible to save energy by using less water at the beginning. But for the "small batcher" with an ordinary cooking apparatus, the most complete conversion is obtained by using the full amount of water right from the start to encourage a rapid rolling boil.)

Next, add 3 measuring spoons -- as provided -- per bushel of MOTHER's Alcohol Fuel Mash Cooking Enzyme (mixed in water) to the mixture and raise the temperature of the mash to 170 deg F (77 deg C), the optimum working environment for the enzyme. Hold the solution at that temperature for 15 minutes while agitating it vigorously.

At this point all the starch available at 170 deg F has been converted to dextrins, so it's time to raise the temperature of the mash to the boiling point. The concoction should be liquid enough to roll at its own rate -- if not, add 2 to 3 gallons of water. Hold the boil for 30 minutes to complete the liquefaction stage. All the starches are now in solution.

Now reduce the temperature to 170 deg F, using the cooling coil, and add 3 more measuring spoons per bushel of MOTHER's Cooking Enzyme (mixed in water). After 30 minutes of agitation at this temperature, all the previously released starches will have been reduced to dextrins, thereby completing primary conversion.

During secondary conversion the dextrins are further reduced to simple sugars (maltose and glucose) by the beta, or -- to be more exact -- glucoamylase enzymes. Because MOTHER's Alcohol Fuel Fermentation Powder contains both the enzymes and the yeast necessary to carry out secondary conversion and proper fermentation simultaneously, you can add 6 measuring spoons per bushel of the fermentation powder (mixed in water) as soon as you've brought the temperature down to 85 deg F (29 deg C) using the cooling coils.

Quinone

rezafahlevi03@gmail.com (thank's for feed me...!!!) — Fri, 11 Jul 2008 08:00:00 +0000

Benzoquinone, or quinone is one of the two isomers of cyclohexadienedione. These compounds have the molecular formula C6H4O2. Orthobenzoquinone is the 1,2-dione, whereas parabenzoquinone is the 1,4-dione.

Orthobenzoquinone is the oxidized form of catechol (1,2-dihydroxybenzene), while parabenzoquinone is the oxidized form of hydroquinone. An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which is oxidized back with a solution of silver nitrate.

Quinone is also the name for the class of compounds containing either benzoquinone isomers as part of their structure. Quinones are not aromatic, but are diketones.

Quinone is a common constituent of biologically relevant molecules (e.g. Vitamin K1 is phylloquinone). Others serve as electron acceptors in electron transport chains such as those in Photosystems I & II of photosynthesis, and aerobic respiration. A natural example of the oxidization of hydroquinone to quinone is the spray of bombardier beetles. Hydroquinone is reacted with hydrogen peroxide to produce a fiery blast of steam, a strong deterrent in the animal world. Quinones can be partially reduced to quinols.

Benzoquinone is used in organic chemistry as an oxidizing agent. Stronger quinone oxidising agents exist; for instance: 2,3,5,6-tetrachloro-parabenzoquinone (also known as p-chloranil) and 2,3-dicyano-5,6-dichloro-parabenzoquinone (also known as DDQ).