The pyrolysis of esters and related compounds

Ramsay, William K (1963) The pyrolysis of esters and related compounds. MSc(R) thesis, University of Glasgow.

Abstract

1. Threshold temperatures in the competitive pyrolysis of vinyl benzoate. An observation by Muir1 suggested that one, or all, of the reactions competing in the pyrolysis of vinyl benzoate may be influenced by metallic catalysts. Further investigation now shows that the decarboxylation reaction →C2) and the rearrangement-cum-decarbonylation →R/C1) are catalysed by the metals present: tin, bismuth, lead, cadmium). This was suspected for the C2 route which was thought to be partially heterogeneous; but the R/C1 route was thought to be completely homogeneous and, therefore, independent of heterogeneous catalysis. While the test to indicate the onset of the R/C1 route was not so satisfactory as that for the C2 scission, the catalytic efficiency of the four metals used was identical in both reactions. 2. Pyrolysis of Ph.CHX2 X = Br, Cl, or CN. Both benzal bromide and benzal chloride pyrolyse at ca. 500° to produce alpha:alpha'-di-x-stilbene, thus: PhCHX2' HX + 1/2 PhXC:CXPh. The bromide produces only the trans isomer, while the chloride produces both cis and trans. It was therefore probable that benzal cyanide would similarly produce alpha:alpha1-dicyanostilbene and from observations the formation of only the trans isomer was indicated. Benzal cyanide did not, however, break down under the above conditions : and even when copyrolysed at ca. 430° with alpha-cyanobenzyl benzoate a compound previously found to produce trans-alphaalpha':-dicyano-stilbene) no substituted stilbene was found. At still higher temperatures ca. 700°) benzal cyanide gave a complex tarry product, not characterized. The failure of benzal cyanide to break down on the same lines as benzal bromide disproves the mechanism proposed20 to account for the presence of alphaalpha'-dicyano-stilbene in the pyrolysate from alpha-cyanobenzyl benzoate. The mechanism was thought to depend upon the formation of the intermediate PhCH?CN)2, thus: [O?CHoPhCN)2] ' PhoCHO + PhoCH?CN)2 HCN + 1/2 CPhCN : CPhCN R It is now believed that the cyanostilbene must be formed by a scission of alpha-cyanobenzyl benzoate, thus: Ph.CO2OCHOPhCN → PhoCO2H 1/2 CPhCN : CPhCN A.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Additional Information: Adviser: P D Ritchie
• Keywords: Organic chemistry
• Date of Award: 1963
• Depositing User: Enlighten Team
• Unique ID: glathesis:1963-73913
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73913