Squaric acid difluoride

Hitherto unknown squaric acid difluoride (3,4-difluoro-3-cyclobutene-1,2-di one) (1a) has been synthesized in 71% yield by gas phase fluorination of sq uaric acid dichloride (1c) with KF at 250 degrees C. (1a) has been characte rized by multinuclear NMR, mass, IR and Raman spectra. The IR spectrum is i n excellent agreement with its ab initio prediction (MP2, 6-311 + G(2d, p)) . The vacuum thermolysis of (1a) at 700 degrees C does not yield the expect ed decarbonylation product FCCF (2a) although the precursor of the latter, F2CCCO, and three C3F4 isomers (propyne, allene, cyclopropene) which are al so found as decomposition products of (2a) have been identified. (C) 1999 E lsevier Science S.A. All rights reserved.