Methyleneketenes and methylenecarbenes. XII. Thermal rearrangement of acetylene

Abstract

Flash vacuum pyrolysis of 1,2,3,4-tetrafluoro-9-methoxy-9,10-dihydro- 9,10-ethenoanthracene[12-¹³C;10,12-D₂], (600°) gives doubly labelled acetylene HC≡¹³CD. At temperatures of 700° and greater, the ethenoanthracene gives a mixture of HC≡¹³CD and DC≡¹³CH. Formation of the acetylene at 600° followed by pyrolysis at 850° confirmed that it is the free acetylene that undergoes intramolecular rearrangement:

                                    _>700^.

                              HC≡¹³CD ↔ DC≡¹³CH

The pattern of labelling in the acetylene was determined by allowing it to react with bromine and examining the resulting 1,1,2,2- tetrabromoethane by p.m.r. and infrared spectroscopy. Mass spectral studies on the tetrabromoethane showed that no significant intermolecular hydrogen exchange takes place up to 1050°.