Cinnamic acid dibromide

Preparation 323.—Cinnamic Acid Dibromide Z-Phenyl-2 3-dibromo-propan acid. ... 

The loss of a bromide ion when situated in a -position to a carboxylate group occurs very readily under mildly basic conditions. Thus in an alternative synthesis of phenylacetylene (Expt 5.24), cinnamic acid dibromide is converted into /1-bromostyrene under the influence of hot aqueous sodium carbonate solution. Dehydrobromination to yield the acetylenic compound is then achieved in the usual manner with potassium hydroxide. 

ArCH = CHBr and ArCH=CRBr, are similarly prepared fro.m substituted cinnamic acid dibromides by heating with alcoholic sodium acetate solution. ... 

Cinnamic acid dibromide (25 g) is placed in an evaporating dish and treated with a 25 % solution (100 ml) of potassium hydroxide in methanol. The mixture is heated on a vigorously boiling water-bath until the methanol is wholly removed. Further methanol (75 ml) is added to the viscous residue and again evaporated off, so as to complete the reaction. When the mass cools, adhering methanol is removed from the pale yellow, granular product by suction. 

In weakly alkaline solution, dehalogenative decarboxylation of /3-halo-carboxylic acids occurs readily . In the case of //-arts-cinnamic acid dibromides, the stereochemical fate of the /3-bromostyrene is determined by the solvent and substituents in the benzene ring (274) . ... 

Dibromo- 2-phenylpropionic acid, cinnamic acid dibromide, i-phenyl- 2-dibromopropionic acid)... 

CeHsCHBrCHBrCOOH -> C6H5CH=CHCOOH A soln. of cinnamic acid dibromide and trimethyl phosphite in toluene refluxed 20 hrs. cinnamic acid. Y 92%.—Similarly trans-Dibenzoylethylene dibromide... 

A more direct approach to acetylenes has been reported which utilizes phase-transfer generated tetrabutylammonium hydroxide to dehydrohalogenate a-halo-olefins or bis-dehydrohalogenate vicinal dihalides. An example of the latter is the reaction of 1,2-dibromo-l-phenylethane in pentane with 50% aqueous sodium hydroxide in the presence of tetrabutylammonium bisulfate. The product, phenylacetylene, is produced in 87% yield in less than an hour by this method (see Eq. 9.11) [27]. The advantage of this approach is apparent when one considers that in the traditional method, jS-bromostyrene (from the dehydrohalogenation and decarboxylation of cinnamic acid dibromide) is heated with KOH at over 200° and the phenylacetylene distills as formed in 67% yield [28]. 

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