science practical

Twelve principles of green chemistry

2020-08-25T23:57:00.002-07:00

Twelve principles of green chemistry

Ans... Here are twelve principles of green chemistry as formulated by P. T anstas and J. C warner,in green chemistry.

1...Prevention:-----

It is better to prevent wast than to treat or Clean up wast aftar it has been created.

2...Atom economy:----

Synthetic methods should be designed to maximize the incoporation of all materials used in the process into the final product

3...Less hazardous chemical synthesis:---

Wherever practical synthetic methods should be designed to use and generate substances that possess little or no toxicity to people or environment

4...Designing safer chemicals :---

Chemical products should be designed to effect their desired function while minimizing their toxicity

5...safer solvent and auxiliaries:---

The use of auxiliary substances (eg. Solvent or separation agents) should be made unnecessary whenever possible and innocuous when used.

6...Design for energy efficiency:---

Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized.If possible, synthetic method should be conducted at ambient temperature and pressure.

7...Use of Renewable feedstocks:---

A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.

8...Reduce Derivatives:---

Unnecessary derivatization (use of blocking groups, protection / de-protection and temporary modification of physical /chemical processes) should be minimized or avoided possible, because such steps require additional reagents and can generate wast.

9...Catalysis:---

Catalysis reagents (as selective as possible) are superior to stoichiometric reagents.

10...Design for Degradation :---

Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.

11...Real time Analysis for pollution prevention:---

Analytical methodologies need to be further developed to allow for real time in process monitoring and control, prior to the formation of hazardous substances

12...Inherently safer chemistry for safer prevention:--

Substances and the form of the substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions and fires

....................... End ......................

Designing a green synthesis

2020-08-25T09:22:00.003-07:00

Designing a green synthesis

Ans. ..... Green chemistry for chemical synthesis address our future challenge in working whit chemicls processes and products by inventing novel reactions that can maximize the desired products and minimize by products , designing new synthetic schemes and apparatus that can simply operations in Chemical productions,The bigning of green chemistry is frequently considerd as a response to the need to reduce the damage of the environment by man-mad materials and the process used to produce them. A quick view of green chemistry issue in the past decade demonstrates man methodologies that protect human helthvand the environment in an economically benifical manner.

Prevention of waste:

Manufacturers try to generate as little wast as possible, through reaction choice ,process designing and recycling. Industries aim to use chemical reactions and process that make the most effective use of available resources and generate the smallest possible amount of wast materials.But can prevention be assessed quantitatively.
One way of measuring the efficiency of a process is to calculate the yield which compares the expected products quantity with the actual amount obtained.
Eg... Is the manufacturing of phenol. It is used to be made from benzene using sulfuric acid and sodium hydroxide in a multi-satage
Process,which ,over all can be expressed as:

The chemicll equation shows that 1mol of benzene (78g)should yield 1 mol of phenol products is found to be about 77 g, givibg a yield of 82%,which may be regardes quit good.
(yield % = mass produced / mass expected x 100%)
However the calculation obscures the fact that the reaction also generates 1 mol (12 g) of sodium sulfite for each mol of phenol produced. This may be acceptable if there is enough demand for sodium sulfite,but if nit ,it presents a serious problem of wast management and adds significantly to costs ,meaning that this may not be the most suitable reaction for manufacturing phenol.

Maximum incorporation of the materials used in the process into the final product(atom economy)

Atom economy:--

The concept of atom economy as developed by Barry Tost consider how much of reactants in Chemical reaction ends up in tje final useful products.The goal of atom economy is to create synthesis in which most of the atoms of the reactants become incorporated into the desire final products leding to lower percentage of wast by products. Atom economy is the concept that evaulates the efficency of chemical transformation, and calculated as a ratio of total mass of atoms in the desired products to the total mass of atoms in the reactants.
Maximum incorporation of the reactants (atom economy) :--
Chemistry globally considers that if the yield of a reaction is abiut 90% , the reaction is good. The percentage of yield is calculated by

One of the fundamental and most important principle of green chemistry is that of atom economy

It is observed that rearrangement and addition reaction are most economical.

claisen rearrangement:--

atom economy %=(134.18/134.18)x100=100%

Addition Reaction :

May atom economical reactions using various transition metal catalysts have been developed (Trost, 1983,1998-200,Trost et al., 200).

Atom economy of catalytic process:

Diels Alder reaction is 100% atom economy reaction as all the atoms of thr reaction are incorporated in the cyclo adduct

palladium catalyzed synthesis of methyl methylacrylate has 100 % atom economy
via green synthesis

The old method of synthesis has only 47% atom economy

Lesa hazardous Chemical syntheses

It is essential to design new synthetic
methods so as to use and generate substances that are not toxic to human life and health.E.g in manufacturing of polystyrene foam sheet, chlorofluorocarbons responsible for O2 depletion, global warming has now been replaced by CO2 as blooming agent
Monasto company has developed a method of synthesizing polyurethanes that totally eliminates the use of phosgene (walden and riley, 1994)

Di-methyl carbonate DMC is good chemical alternative as methylating reagent for toxic methyl halid or methyl sulphate. The reaction of DMC reactive methylene compounds produce monomethylated derivatives with selectivity.

Short note on green chemistry as sustainable development

2020-08-25T03:26:00.002-07:00

Short note on green chemistry as sustainable development

green chemistry which was established about two decades ago has attracted much attention .it reflects efforts of academia and Industry to address the challenge related to sustainable development of the chemical industry and continuous progress is being made both in academia and industry. Briefly green chemistry is the utilization of a set of principles to reduce or eliminate the use of generation of Chemical products. Green chemistry is a multidisciplinary field and covers are such as synthesis , solvents , catalysts , raw materials ,products , and efficient processes, as shown in figure

Important examples of green chemistry including phasing out the use of chlorofluorocarbons (CFCs) in refrigerants , which have played a role in creating the ozone hole , developing more efficient ways of making pharmaceuticals , including the well known painkiller ibuprofen and chemotherapy drug toxol, and developing cheaper , more efficient solar cells
Sustainable development is one of the most frequently used term in today's political debate. Our current understanding of sustainable development as regulatory idea was basically defined by the agenda 21:,"sustainable development is development that meets the need of the present with out comparaising the ability of future generation to meet there own needs." as a cosiquence all industrial and political action should be reflected in the light of there social economic and ecological sustainability.

Green solvents

2020-08-25T03:19:00.003-07:00

Green solvents

Organic solvents are toxic and volatile which are harmful to human health and creates pollution in environment Therefore it is necessary to replace these solvents by safer solvents like ionic liquids, supercritical CO2 or supercritical water and also solvent free system that utilizes the surface or interiors of clay zeolites, silica and alumina.Supercritical CO2 fluid is now becoming important commercial and industrial solvent for Chemical separations because of low toxicity and non inflamability. Ionic liquids (Welton 199 Holbery and seddon, 1999 Seddon 1997)are substances composed of cation and anions. Ionic liquids have emerged as green solvents because they have no measurable vapour pressure and that wide range of chemical reactions can be performed in them. Commonly used ionic liquids are those with alkyl ammonium, alkyl phophonium, N-alkyl pyridium cautions and Cl, Br-,I-,BF4- anions .Ionic liquids find their useful and important application from hydrogenation to biocatalytic reactions
Near critical water offers outstanding performance as benign solvents for both organic and ionic compounds .Friedal - Craft's acylation requires Lewis acids but in near critical water, phenol could be converted with acetic acid to produce 2-hydroxy acetophenone, 4 -hydroy acetophenone and phenyl acetate without addition of an acid catalyst.

Liquid polymers, flurous solvents, eutectic mixtures etc have potential to be used as green solvents.

Green catalysts

2020-08-25T03:15:00.001-07:00

Green catalysts

Conventional catalysts are hazardous, corrosive and toxic in nature, therefore, it is pertinent to use green catalysts, which is environmentally benign and has maximum selectivity for product formation.Now a days conventional catalysts are replaced by silica alumina catalysts for production of alkyl benzene. Zeolites ,clayzic titanium silicate are few examples among other green catalysts
Bio-catalysts transformations represent an immense potential in organic synthesis.Enzymes occupy a prominent
place among bio catalysts. Zeolites themselves account for more than 40%of acid - based catalysts.

How does microwave increase the rate of reaction.

2020-08-25T02:59:00.005-07:00

How does microwave increase the rate of reaction.....

Any Chemical reaction begins with A and B which have the certain energy state as ER as shown in diagram. These reactants react in exact geometrical orientation to get activated to the higher energy transformation i.e ETS. Thus activation energy Ea is given by Ea=ETS - ER. Thus activation energy becomes very important which system absorb form environment.once the reaction absorb sufficient amount of activation energy it react and will return to the lower energy states i.e Ep - the product of reaction A-B. 5 microwave energy is such a tool which will not affect the activation energy but it provide a great momentum to complete the reaction more quickly and in more efficiently as compared to conventional heating. In each cycle of electromagnetic energy the microwaves will transfer energy 10-9 sec whereas the kinetic molecular relaxation will take 10-5sec.This indicates that energy transfer is faster than the molecular relaxation .
This helps to create the high instantaneous temperature and non-equilibrium condition which have a great impact on the kinetic of the reaction.this helps to increase the reactant rate in less time with greater yield.