Reactions and characterisation of aromatic carboxylic acids

Aromatic carboxylic acids are usually crystalline sohds, bum with a smoky flame, and are generally sparingly soluble in water. They may be det ed and characterised as already described under Aliphatic Carboxylic Acids (Section 111,85). 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0 5 g. of the acid with 3 g. of soda lime, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from salicylic acid, anisole firom anisic acid, toluene from toluic acid, etc. 

The melting points of the derivatives of a number of selected aromatic carboxylic acids are collected in Table IV, 175. 

Acid B.P. M.P Anilide Tolul- dlde Amide Bromo- pbenacyl Ester Nltro- benzyl Ester Pbenyl- pbenacyl Ester S-Benzyl- wo-tbi- uronlum Salt Other Oeilvatlves 

AnlUde Tolui- dlde 1 Amide p Bromo- phenacyl Ester /)-Nltro- benzyl Ester p-Phenyl phenacyl Ester S-Benzyl- Ao-thi- uronium Salt Other Derivatives 

P Anilide Amide phenacyl Ester benzyl Ester phenacyl Ester uronlum Salt  

P Anilide Amide phenaeyl Ester benzyl Ester pbenacyl Ester Other Derivatives 

---