P Toluidine

Prepared by mononilrating toluene, as a 40% constituent of the mixture of isomers. It is reduced to p-toluidine with iron and hydrochloric acid. 

A) PRIMARY AROMATIC AMINES. RNH. Aniline, o-, m-, and p-toluidine (and other nuclear-substitiited anilines) 1- and 2-naphthylamines. (For note on Aliphatic Amines, cf. p. 375 )... 

Physical properties. Majority are liquids except p toluidine and 1- and 2-naphthylamine. All are colourless when pure, but rapidly darken on exposure to air and light. All are very sparingly soluble in water, but dissolve readily in dilute mineral acids (except the naphthyl-amines, which are only moderately soluble in adds). They form colourless crystalline salts e.g., CjHjNH2,HCl) which are soluble in water these aqueous solutions usually have an add reaction owing to hydrolysis, and give the reactions of both the amine and the acid from which they are derived. Addition of alkali to the acid solution liberates the amine. 

Basic Component. The filtrate from (a), or the HCl extract from b), now contains the basic component in the form of its hydrochloride. Add 30% aqueous NaOH solution until alkaline to litmus. Cool, and scratch the sides of the vessel with a glass rod a white precipitate indicates a solid amine, e.g, p-toluidine or a naphthylamine. Dilute, filter off, wash well with water (recrystallise if necessary), dry and identify. 

TEST Aniline 0- toluidine m-> toluidine P-. toluidine I- naphthyl- amine 2- naphthyl- amine mono- methyl- aniline diphenyl- amine dimethyl- aniline triphenyl- amine... 

Many chloroplatinates separate from aqueous solution with water of crystallisation. If this is suspected, the chloroplatinate should be dried to constant weight in the oven before analysis, to ensure elimination of water of crystallisation. Aniline, p-toluidine and pyridine all give anhydrous chloroplatinates, and can be conveniently used in the above determination no attempt should be made to recryrtallise their chloroplatinates. 

Anilides and p-toluidides may also be prepared directly from the acide% by heating them with aniline or p toluidine respectively ... 

Place 1 0 g. of the monobasic acid and 2 g. of aniline or p-toluidine in a dry test-tube, attach a short air condenser and heat the mixture in an oil bath at 140-160° for 2 hours do not reflux too vigorously an acid that boils below this temperature range and only allow steam to escape from the top of the condenser. For a sodium salt, use the proportions of 1 g. of salt to 1 5 g. of the base. If the acid is dibasic, employ double the quantity of amine and a reaction temperature of 180-200° incidentally, the procedure is recommended for dibasic acids since the latter frequently give anhydrides with thionyl chloride. Powder the cold reaction mixture, triturate it with 20-30 ml. of 10 per cent, hydrochloric acid, and recrystallise from dilute alcohol. 

The above simple experiments illustrate the more important properties of the anhydrides of aliphatic acids. For their characterisation, the reaction with aniline or p-toluidine is frequently employed. Alternatively, the anhydride may be hydrolysed with dilute alkali as detailed under Acid Chlorides, Section 111,88, and the resulting acid characterised as in Section 111,85. 

Anilides or p-toluidides of acids from esters. Esters are converted into the corresponding anilides or p-toluidides by treatment with anilino- or with p-toluidino-magnesium bromide, which are readily obtained from any simple Grignard reagent and aniline or p-toluidine ... 

Alternatively, add a solution of 4 5 g. of p-toluidine in dry ether to the Grignard reagent prejjared from 1 0 g. of magnesium as detailed above. Then introduce 1 0 g. (or 0 02 mol) of the ester and proceed as described lOr anihdes. 

Shake for 10-15 minutes. Extract tliealkahiie solution with ether to remove excess of p-toluidine, acidify, filter, and recrystalUse the residue as in (i). 

Dissolve 1 g. of the sulphonic acid or its sodium salt in the minimum volume of boiling water and add a saturated aqueous solution of 1 g. of p-toluidine hydrochloride. Cool, Alter off the precipitate of the p-tolu-idine salt, and recrystallise it from hot water or from dilute ethanol. 

For the preparation of w-bromotoluene, the following sequence of reactions from p-toluidine may be used ... 

The boron trifluoride is absorbed in sodium hydroxide solution. Similarly p-toluidine p-CH3C,H4NHj 3uelds />-fluorotoluene p-CH3CgH4F. 

Dissolve 36 g. of p-toluidine in 85 ml. of concentrated hydrochloric acid and 85 ml. of water contained in a 750 ml. conical flask or beaker. Cool the mixture to 0° in an ice-salt bath with vigorous stirring or shaking and the addition of a httle crushed ice. The salt, p-toluidine hydrochloride, will separate as a finely-divided crystalline precipitate. Add during 10-15 minutes a solution of 24 g. of sodium nitrite in 50 ml. of water (1) shake or stir the solution well during the diazotisation, and keep the mixture at a temperature of 0-5° by the addition of a httle crushed ice from time to time. The hydrochloride wUl dissolve as the very soluble diazonium salt is formed when ah the nitrite solution has been introduced, the solution should contain a trace of free nitrous acid. Test with potassium iodide - starch paper (see Section IV,60). 

In a 1 litre flask mix 53 -5 g. of p-toluidine and 400 ml. of water, and then add cautiously 98 g. (53 6 ml.) of concentrated sulphuric acid warm until the p-toluidine dissolves. Cool the flask in a bath of ice and salt to 0-5° add about 100 g. of crushed ice to the contents of the flask in order to accelerate the cooling. Add slowly and with frequent shaking a solution of 35 g. of sodium nitrite in 60 ml. of water until a slight excess of sodium nitrite is present (.see Section IV,60) keep the temperature of the mixture below 10°. 

Methylaniline Ethylaniline n-Propylaniline n-Butylaniline Benzylaniline 2 -MethyIbenzylamine N-Ethylbenzylamine 2 -Methyl o-toluidine N-Methyl m-toluidine 2 -MethyI p-toluidine N-Ethyl o-toIuidine N-Ethyl m-toIuidine 2S -Ethyl p-toluidine 2 -MethyI a-naphthylamine N-Methyl p-naphthylamine N-Phenyl- a-naphthylamine 2 -Phenyl-P-naphthylamine... 

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