Hell-Volhard Zelinsky Halogenation

The Hell-Volhard Zelinsky reaction is a halogenation reaction at the alpha carbon of a carboxylic acid. The reaction is initiated by a catalytic amount of PBr3, after which one molar equivalent of Br2 is added. The carboxylic OH is replaced by the Br resulting in a carboxylic acid bromide. The acyl bromide then tautomerizes to the enol so it can brominate again at the alpha carbon. The general mechanism of the reaction is shown below:

A reaction that employs the use of the Hell-Volhard Zelinsky mechanism is the synthesis of Dimethylketene. Its IUPAC name is 2-methyl-1-propen-1-one and it has a molecular formula of C4H6O. Its structure is shown below:

The physical properties of dimethylketene are:
- molecular weight: 70.09g/mol
- boiling point: 34*C
- density: 0.775g/cm^3

The reaction scheme for the synthesis of this compound from its starting material is shown below:

The starting material is 2-methylpropanoic acid which is catalyzed by the PBr3 resulting in the substitution of the carboxylic OH by a Br and an addition of Br at the alpha carbon. The second step in the procedure is a different kind of reaction that results in the final product dimethylketene. The true product of the Hell-Volhard Zelinsky reaction is the 1,2-dibromo-2-methylpropanone. This compound has a molecular weight of 230.09g/mol.

As of to the physical properties of the compound, I could not find any information.

References:
http://www.qwiki.com/q/#!/Hell-Volhard-Zelinsky_halogenation
http://www.chemspider.com/Chemical-Structure.120167.html