HILL AND CORNELISON. 



CROTONOLACTONES. 



xc 



xc = 



xc 



xc 



CBr 



X 



/ 



CH 



CBr 2 



X 

 / 



CHBr 



+ Br 2 



XC 



XC- 

 XC 



CBr 2 



X 

 / 



CHBr 



+ H 2 



XC- 



CO 



x o 



/ 

 CHBr 



+ 2HBr 



It has already been said that two isomeric monosubstituted crotono- 

 lactones may be made by appropriate means from the disubstituted 

 pyromucic acids containing the halogens in the /3 and S positions. By 

 heating these substituted pyromucic acids with mineral acids the brom- 

 and chlorcrotonolactones melting at 58° and 26° respectively may be 

 made. The reaction is evidently perfectly analogous to the decompo- 

 sition of the trisubstituted pyromucic acids under like conditions which 

 has just been discussed. The carboxyl group is replaced by hydro- 

 gen with the loss of carbonic dioxide and the substituted furfuran thus 

 formed then passes into the lactone as before : 



+ co 2 



+ HBr 



The ^-substituted lactones which are thus formed may be made much 

 more conveniently by the partial reduction of the disubstituted lac- 

 tones. In order to prepare the monohalogenized crotonolactones with 

 the halogen in the a position from the /38-dichlor- and dibrompyromucic 

 acids, derivatives of maleic acid must first be formed. The first step 

 in the reaction is the formation of a trisubstituted furfuran through 

 the replacement of the carboxyl by bromine : 



XC = 



HC = 



0+ C0 2 + HBr 



Through the addition of bromine with the shift of the double bond, 

 as before, 



