Introduction
According to a German article from the late 1920's1, 2-phenylpropanal can be rearranged with either mercuric chloride (HgCl2) or sulfuric acid (H2SO4) to form the isomeric phenyl-2-Propanone (P2P), an important intermediate in the synthesis of amphetamines. 2-Phenyl-propanal is an unwatched industrial chemical, which is used in the perfume industry, but it can also be made from α-methylstyrene.
The CAS number for 2-phenyl-propanal is [93-53-8], and a few of its synonyms are Hydratropic aldehyde (Hydratropaldehyde); 2-Phenylpropionaldehyde; Cumenealdehyde; and α-methyl phenylacetaldehyde.
Other ways of performing this rearrangement include isomerization of 2-phenylpropanal to phenyl-2-propanone in up to 87% yield by passing its vapor over an iron zeolite catalyst bed at 500°C2, followed by condensation of the vapors and redistilling the P2P.
Even if the method below which uses mercuric chloride is higher yielding than the one using cold sulfuric acid, I would definitely reccommend the one with sulfuric acid, as it is much cheaper to use, and is not disastrous for your health or the environment. 60g of mercuric chloride contains 45g of mercury, enough to poison a medium-sized lake if released into the environment, and if you happen to ingest it yourself, it will accumulate in your body.
Experimental
Method A
30g of 2-phenylpropanal is heated together with a mixture of 60g mercuric chloride (HgCl2, 1 eqv) and 450ml 75% ethanol in a pressure-safe sealed glass container for 4.5h at 100°C in a boiling water bath, during which time a precipitate forms. Water is added, and the solution is steam-distilled (during which operation the precipitate redissolves). The distillate is extracted with ether, dried, and the solvent is evaporated. The oily residue is then vacuum distilled with a fractionating column (bp 92-101°C/14mmHg) to collect phenyl-2-propanone in at least 80% yield.
When 0.1 equivalents of HgCl2 was used, only 10% phenyl-2-propanone was formed, the rest consisted of unchanged aldehyde.
Method B
2-phenylpropanal (9 g) is slowly added with good stirring during 35 minutes to 40 mL concentrated sulfuric acid, while the temperature of the reaction mixture is kept at -16°C. After all the 2-phenylpropanal has been added, the mixture is allowed to stand at the same temperature for another 15 minutes, and then the mixture is poured onto crushed ice (100-150g is probably a suitable amount). When the ice has melted, the organics are extracted from the water phase by 3x50ml diethyl ether, the pooled organic phases dried over MgSO4, the ether distilled off and finally the residue is vacuum distilled (bp 91-96°C at 11 mmHg) to give 5.6g (62%) of phenyl-2-propanone.