Nitroso-o-cresol

While the mtrosation of phenols occurs at least as readily as that of tertiary aromatic amines such as dimethylaniline, the conditions must be very carefully controlled owing to the ease with which most phenols oxidize. For this reason a higher proportion of tarry by-products is formed and the yields are smaller than in tiie case of the dialkylanilines. Taking o-cresol as a typical example of a phenol with an unsubstituted para- position, the main product of the reaction is -nitroso-o-cresob 

unless some substance is at hand to bind the hydrochloric acid as fast as formed, exceedingly complex mixtures are obtained from which it is virtually impossible to isolate pure products mesityl oxide, for instance, boiling at practically the same point as mono-chloroacetone. Fritsch1 found that small pieces of marble were very satisfactory, as these reacted at once with the hydrochloric acid liberated, and his method is accordingly the basis of that given below. 

The upper layer of acetone and its chlorination products is fractionated with the aid of a good distilling column, the monochloroacetone boiling at 118-20°. The yield is r6.8 g., plus an additional 5 g. on refractionation of the lower and upper fractions. 

The chloro-acetones are extremely irritating, both in vapor form and if dropped on the skin. Gloves should be worn and all operations conducted under the hood. This applies to the next experiment as well. 

The method used depends upon the fact that although acetic acid and its homologs react with difficulty with bromine, the anhydrides and acid bromides readily yield bromo substitution products.8 

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Another very convenient method which gives a homogeneous product in good yield involves the oxidation of /j-nitroso-o-cresol to the p-mtro derivative, as given by Borsche and Berkhout,8 except that almost quantitative yields are obtained m the cold instead of on boiling as recommended by these authors... 

Solid sodium nitrite (35 g., 0.51 mole) is added to a stirred suspension of 27 g. (0.25 mole) of o-cresol in 2 1. of ice-water slurry. A solution of 9.5 ml. of concentrated sulfuric acid in 200 ml. of water is added over a 1-hour period, the temperature being held below 5° by the further addition of ice. The mixture is allowed to stand for 2 hours, and the nitroso compound is filtered off and washed with water. Recrystallization of a small amount of the product from benzene gives pure 2-methyl-4-nitrosophenol, m.p. 136°. 

C7H6N604 5-(N-methyl-N-nitroso)amino-3-(5-nitro-2-fur 41735-28-8 25.00 1.6632 2 10525 C7H7CIO 5-chloro-o-cresol 5306-98-9 19.83 1.1954 2... 

Substituents in the ortho- or meta-position to a hydroxyl group usually do not interfere. Thus o- and m-cresol afford the 4-nitroso derivatives (OH = l).292 / -Substituted phenols react differently, if at all p-cresol, for instance, is nitrated in the ortho-position to the hydroxyl group by nitrous acid.292... 

Nitroso compounds are formed as intermediates in this reaction. Yields from sulfonic acids, carboxylic acids, and nitro compounds, amongst others, are poor,424 but those from tertiary amines and phenols are often very good,423,426 although naphthols give only the nitroso derivatives for example, yields are 70% from A,iV-diethylaniline,423 96% from phenol,426 98% from o- or 7W-cresol,426 95% from chlorophenol,426 and 75-85% from o-hydroxybenzene-sulfonic acid 428 the diazonium group enters para to the NR2 or OH group. 

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