REACTIONS AND IDENTIFICATION 371 GENERAL REACTIONS. 1. Many quinones are volatile in steam. 2. Give characteristic reduction products depending upon reagent used. 3. Give colorations with NaOH solution. 4. Oxidation depending upon oxidising agent used. 1. Volatility in steam. Add about o-i g. of benzoquinone to 3 ml. of water in a test-tube and boil gently. The benzoquinone dissolves to give a yellow solution, which rapidly darkens in colour. Note the irritating and characteristic odour of benzoquinone which has volatilised in the steam. Also given by p-toluquinone and i,4~naphthoquinone but not by the other quinones mentioned above. 2. Reduction, (a) By sulphurous acid. Benzoquinone, p-toluquinone, i,2-naphthoquinone are readily reduced by SO 2 ultimately to the dihydroxy-compound. Thus benzoquinone gives colourless hydro-quinone or quinol, p-C 2 H 4 (OH) 2 . To a cold aqueous solution of benzoquinone, add i drop of sulphurous acid solution (SO 2-water): the solution turns deep green-brown owing to the intermediate formation of quinhydrone,
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