Proton resonance spectra were obtained at 100 MHz on a Varian Associates HRlOO spectrometer. Probe temperatures were calibrated with a copper-constantan thermocouple in a dummy sample tube. Methylene chloride, purified and stored over Linde Molecular Sieve 4A in a container on the vacuum line, was used as internal reference, Tetramethylsilane is unsuitable since it slowly reacts with arsenic pentafluoride to yield trimethylsilyl fluoride. Arsenic pentafluoride (Ozark-Mahoning) and anhydrous sulfur dioxide (Matheson) were stored over Pz05 in bulbs on the vacuum line. Acetyl fluoride was prepared according to the literaturelo and kept frozen when not being used. It was necessary to carefully bake the vacuum system prior to sample preparation in order to get adequately pure samples. If this precaution is not followed eq 1 is not obeyed, presumably because of other exchange pathways for the acetyl ion. Throughout this investigation only samples which obeyed eq 1 were used. The occasional sample which deviated was discarded and another prepared. The extent of agreement with eq 1 is shown in part by Table I. The data were fitted by least-square techniques and the listed errors are standard deviations. displace the dissociation equilibrium and lower the concentration of acetyl ions by the common ion effect. This should then cause a reduction in the exchange rate of acetyl hexafluoroarsenate. Unfortunately those hexafluoroarsenates which are soluble in sulfur dioxide exist almost entirely as the ion pair in solution. Therefore a negative result would not disprove the mechanism but a reduction in rate would be confirming evidence. It was found that addition of an equimolar quantity of tetra-n-butylammonium hexafluoroarsenate had no effect on the rate of exchange.If the two different states of the acetyl ion involve a change in solvation the mechanism or rate of the reaction might change upon changing solvent. Acetyl hexafluoroarsenate is essentially insoluble in CHzC12 and S02F2. A minor change in solvent was attempted by addition of another salt, tetra-n-butylammonium perchlorate. A rearrangement reaction occurred to yield acetyl perchlorate as neutral molecules. Its proton resonance peak is in the same position as those previously reported for acetyl complexes.e No exchange reaction was observed between acetyl per-(10) C. W. Tullock and D. D. Coffrnan, J . Org. Chem., 25, 2016 (1960).Abstract: Many organomercuric halides react with dicobalt octacarbonyl in tetrahydrofuran solution at room temperature to give the ketone (RzC=O) derived from R in RHgX, Hg[Co(CO)4]~, Co(I1) halide, and carbon monoxide. The reaction proceeds rapidly and is of good preparative utility. The scope and limitations of this new ketone synthesis have been defined and the probable mechanism involves the following steps : solvent-induced redox disproportionation of dicobalt octacarbonyl to give THF Co(C0)4+ and CO(CO)~-; nucleophilic displacement of halide ion from mercury by the latter; electrophilic cleavage of the C-Hg bond in the RH~CO(CO)~ form...
tween log k (rate constant) and the ionization potential of RC6HS. These correlations are gathered into a single Figure 2 by plotting log (k/ko) where ko is the rate for R = H. Since we have established the linear re--2'4 i 1 Figure 2. A plot of log (k/ko) for the solvolysis rates of p-RC6H4-(CH&C(CH&Cl(O), and pRCeH4CHzC(CHa)zC1 (A) against the ionization potential (eV) of RCeH5 (R = H, CHa, OCHZ). C(CH8)zCHzOBs (e), P-RCeHaCHzCHzOTs (O), p-RCeHpClationship for R = H, CH,, and C H 3 0 between the ionization potential and (p-RCeHSCHz)3B charge-transfer transition energy, Figure 2 is also a correlation of log (k/ko) with ECT. It should be noted that the slopes of the correlation lines in Figure 2 correspond to that expected from relative importance of neighboring group participation by the phenyl ring in the solvolysis transition states. The correlation in Figure 2, which involves 12 points, implies that the mechanism by which R stabilizes the excited state of (p-RC6H4CH2),B is similar to that by which the solvolysis transition state of the /3phenylalkyl tosylates, etc., are stabilized. Although each of the four linear relationships in Figure 2 is defined by only three points, no other substituent parameter such as Hammett Q or IS+ places the C H 3 0 on the lines defined by H and CH3. Sir:Recently we reported a synthesis of symmetrical ketones by the reaction of organomercuric halides or diorganomercurials with dicobalt octacarbonyl at room temperature in THF solution.' The yields of ketones were in general quite good, and in the case of diary1 C02(CO)8RHgX e Rz-0ketones they were excellent. organocobalt intermediates was indicated A mechanism involving COz(C0)8 + THF + THF*CO(CO)4+ + Co(C0)r RHgX + CO(C0)r-+ RHgCo(C0)d + X-RCo(CO)4 + RCOCo(C0)a + RzC=O + CO~(CO)T Reactions 1 and 2 represent a stoichiometric utilization of dicobalt octacarbonyl. More practical and economical would be a reaction in which the stoichiometric reagent is carbon monoxide and the relatively expensive dicobalt octacarbonyl is used in only catalytic quantities (eq 3). We report here concerning the realization of such a ketone synthesis. lCoa (CO) 81RzHg + CO -RzC=O + Hg (3)Our new catalytic ketone synthesis is based upon our previously developed reaction of diorganomercurials with dicobalt octacarbonyl (eq 2). In order to make this process catalytic, a method for the conversion of the unreactive H~[ C O ( C O )~]~ to the active reagent, COZ-(CO)s, must be available. Italian workers2 have reported photochemical reactions of Hg[Co(CO)& with acetylenes, in which photolysis of the mercury compound served to release dicobalt octacarbonyl; e.g., eq 4. This observation suggested to us that reaction 1 or 2 could be made catalytic in dicobalt octacarbonyl by irradiating the reaction mixture with an ultraviolet source while the reaction progressed. Our subsequent experiments showed that such was the case.(1) D. Seyferth and R.
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