• question_answer 66) How can you apply green chemistry for the following : (i) to control photochemical smog (ii) to avoid use of halogenated solvents in dry cleaning and that of chlorine in bleaching (iii) to reduce use of synthetic detergents. (iv) to reduce the consumption of petrol and diesel.

(i) The most straight forward way to reduce or prevent the formation of photochemical smog is to minimise the release of oxides of nitrogen and hydrocarbons to the atmosphere. The following methods can be applied to minimise the oxides of nitrogen and hydrocarbons. (a) By fitting efficient catalytic converters in automobiles, the harmful gases are converted catalytically into harmless gases. (b) By spraying certain compounds into the atmosphere which generate free radicals that readily combine with the free radicals that initiate the reactions forming toxic compounds of   the   photochemical   smog.   The   compound diethyl hydroxylamine has been found to possess smog inhibiting property. (c) Certain plants such as pinus, jiniparus, pyrus, vitis, etc., can metabolise oxides of nitrogen. (ii) Solvents used to dry clean clothes are usually chlorinated compounds which are carcinogen. Suitable detergents which work in liquid carbon dioxide have been discovered to replace the chlorinated compounds. For bleaching of clothes in laundry, ${{H}_{2}}{{O}_{2}}$ and not $C{{l}_{2}}$ is used which gives better results and is not harmful. Earlier, $C{{l}_{2}}$ gas was used for bleaching paper. Chlorine is highly toxic in nature. Its use has been replaced by ${{H}_{2}}{{O}_{2}}$ in presence of a suitable catalyst. (ii) To reduce the use of synthetic detergents as cleaning agent, emphasis should be made on the use of soaps prepared of vegetable oils. The vegetable oils are biodegradable while detergents do not undergo biodegradation. (iv) Instead of petrol and diesel, the use of CNG (Condensed Natural Gas) and LNG (Liquefied Natural Gas) has been preferred as they are pollution free fuels. The other sources such as hydrogen, ethyl alcohol, etc., can be tried in place of petrol and diesel.