Site of gas-phase methylation of methyl acetoacetate

✍ Scribed by J.-P. Morizur; I. Martigny; J. Tortajada; S. Geribaldi

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 149 KB
• Volume: 25
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210250120

✦ Synopsis

OMS Letters

Dear sir,

SITE OF GAS-PHASE METHYLATION OF METHYL ACETOACETATE

Gas-phase methylation of ketones(13) and esters (2) have been recently investigated.

In the present study, we report the preliminary results on methyl cation transfer reaction to methyl acetoacetate 1 under low and high pressure conditions by using ion cyclotron resonance (ICR) and mass spectrometric techniques. The reactant ions are generated from methyl chloride. 0-keto esters are compounds of interest by the expected competitive cationization at the two carbonyl sites. In addition they are characteristically an equilibrium mixture of tautomers, i.e. of the keto ester 1 and the corresponding keto-enols le and le' (scheme 1).

On the basis of l H NMR and 13C NMR we conclude that only the two forms 1 and le are present in solution. The enol content determinated by photoelectron is roughly 40% between 65 and 200°C.

In order to identify the gas-phase methylation product(s) of 1 a+"d l e we have compared collision induced dissociation (CID) spectra of the [CgHl 031 ions produced methylation (scheme 2, Table 1).

under chemical ionization (CI) conditions with those of ions a to d t 21 at model 0and Cscheme 2