Question

A compound A (C6H6) undergoes catalytic hydrogenation over Lindlar catalyst to give a compound B, which in turn undergoes ozonolysis followed by workup with aqueous H2O2 to yield succinic acid and two equivalents of formic acid. In the absence of a catalyst poison, hydrogenation of A gives hexane. Propose a structure for compound A.

Answer 1

Answer:

                   Hexa-1,5-diyne is the correct name for Compound-A.

Explanation:

                    This problem was solved using following concepts;

(1) Partial Hydrogenation:

                                          One should always keep in mind that Lindlar Catalyst is used for the partial hydrogenation of Alkyne in order to convert alkynes into alkenes. If the poisoned catalyst is not used then the full hydrogenation will result in the formation of corresponding alkanes like in this case the hexa-1,5-diyne when hydrogenated without converts into hexane as shown in scheme attached.

(2) Ozonolysis:

                        Ozonolysis process was used to characterize alkenes. Upon ozonolysis the alkene were broken down at double bonds and the corresponding acids were obtained depending upon there carbon length. Hence, in this case the succinic acid shows that the starting material (i.e. hexa-1,5-diene) has two double bond with 4 carbon atoms in middle and two carbon atoms at terminals as two moles of formic acids are formed.