P Nitrobenzyl cyanide

In a i-l. round-bottom flask are placed too g. of -nitrobenzyl cyanide. A solution of 300 cc. of concentrated sulfuric acid (sp. gr. 1.84) in 280 cc. of water is prepared, and two-thirds of this solution is poured on to the p-nitrobenzyl cyanide. The mixture is shaken well, until the solid is all moistened with the acid. Any solid material sticking to the walls of the vessel is now washed down into the liquid with the remainder of the acid, the flask is attached to a reflux condenser, then set, without shaking, over a 10-cm. hole in a large sheet of asbestos board which rests on a tripod, and heated until the mixture boils. The boiling is continued for fifteen minutes. 

Nitrobeozyl alcohol, 882 m-Nitrobenzyl alcohol, 881 p-Nitrobenzyl bromide, 961 p-Nitrobenzyl cyanide, 751, 763 p-Nitrobenzyl esters, 362 ... 

Experimental details for the nitration of benzyl cyanide are also included (Expt 6.21). The product is largely p-nitrobenzyl cyanide (some of the ortho isomer is also formed) the cyanomethyl substituent (as a substituted alkyl group) is thus an ortho/para directing and weakly activating group. 

Place a mixture of 275 ml of concentrated nitric acid with an equal volume of concentrated sulphuric acid in a 2-litre three-necked flask, fitted with a thermometer, a mechanical stirrer and a dropping funnel and assembled in the fume cupboard. Cool the mixture to 10 °C in an ice bath, and run in 100 g (98 ml, 0.85 mol) of benzyl cyanide (Expt 5.157) at such a rate (about 1 hour) that the temperature remains at about 10°C and does not rise above 20 °C. Remove the ice bath, stir the mixture for 1 hour and pour it on to 1200g of crushed ice. A pasty mass slowly separates more than half of this is p-nitrobenzyl cyanide, the other components being the ortho isomeride and a variable amount of an oil. Filter the mass on a sintered glass funnel, press well to remove as much oil as possible and then dissolve in 500 ml of boiling rectified spirit. The p-nitrobenzyl cyanide crystallises on cooling. Filter this off at the pump and recrystallise from 80 per cent ethanol. The yield of p-nitrobenzyl cyanide, m.p. 115-116 °C, is 75 g (54%). Another recrystallisation raises the m.p. to 116-117°C. 

Stopped flow and continuous flow methods [11] have been used to follow proton transfer reactions with half-lives in the millisecond range. The stopped flow method which is more popular is essentially a device for mixing the reactants rapidly (typically in one millisecond) together with some means of observing the fast reaction which follows. Proton transfer from p-nitrobenzyl cyanide to ethoxide ion in ethanol/ether mixtures at —77 °C was studied in this way [12]. The reaction was followed spectrophotometrically. The most rapid reaction occurred with ti/2 ca. 2 x 10 2 sec although the equipment was suitable for following reactions with f1/2 ca. 2 x 10 3 sec. A similar method has been used to measure rates of proton transfer between weak carbon acids (for example, triphenylmethane) and bases (for example, alkoxide ions) in dimethyl sulphoxide [13], A continuous flow apparatus with spectrophotometric detection was used [14] to measure rates of ionization for substituted azulenes in aqueous solution (4), reactions for which half-lives between 2 and 70 msec were observed. 

For p-nitrobenzyl cyanide (pK° 13.4) [117] kinetic results were obtained [19] which are similar to the slow proton transfers described for nitroparaffins and ketones. In aqueous solution rate coefficients for amine catalysed detritiation give a Bronsted plot with slope 13 = 0.61 and the rates of the thermodynamically favourable recombination of the car-banion with ammonium ions vary between ca. 103 and 10s 1 mole-1 sec-1. In 80/20 (v/v) ethei ethanol at —77°, a value j3 = 0.49 was observed for catalysis by phenolate ions [12]. The p-nitrophenyl group in this cyanocarbon acid considerably alters the proton transfer behaviour. 

Derivation Hydrolysis of p-nitrobenzyl cyanide with 50% sulfuric acid. 

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