this reactio is also called Borodine Reaction
 
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The silver(I) salts of carboxylic acids react with halogens to give unstable intermediates which readily decarboxylate thermally to yield alkyl halides. The reaction is believed to involve homolysis of the C-C bond and a radical chain mechanism.
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it is recation for preparation  for alkyl bromide
in this we react silver salt of acid with Br2 in presence of CCl4 and we get alkyl bromide + AgBr + carbon dioxide
fluorine and chlorine does not give this reaction and in case of iodine ester is major product
it has radical mechanism
 
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SIze of alkyl group is inveresly proportional to the yield of product
						

							
look in case of  dependency over the carbon atoms it is
10RX>20RX>30RX
 
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and in this reaction the number of carbon is decreased be 1
						

							
and in the case of the reaction with the halides the stability is there of Br2 only in presence of CCl4
here CCl4 is the non polar solvent 
 
						

							
here Fluorine will not be used because of its more electronegativity
here chlorine is not used because of its more bond dissociation enthalpy
and finally iodine is not used beacuse it gives ester and iodine as the majors
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