Long-chain ketones

Another ester synthesis employs the reaction of a long-chain ketone and pentaerythritol in xylene or chlorobenzene (14). Mixed esters have been produced using mixed isostearic and cyclohexane carboxyUc acids in trihromophosphoric acid, followed by reaction with lauric acid (15). 

This procedure has been used with good results to prepare certain long-chain ketones that are precursors of pheromones.204... 

Raven, A. M., van Bergen, P. F., Stott, A. W., Dudd, S. N., and Evershed, R. P. (1997). Formation of long-chain ketones in archaeological pottery vessels by pyrolysis of acyl lipids. Journal of Analytical and Applied Pyrolysis 40 267-285. 

Prahl, F.G., and S.G. Wakeham. 1987. Calibration of unsaturation patterns in long-chain ketone compositions for paleotemperature assessment. Nature 320 367-369. 

Oxidation of aliphatic ketones in trifluoroacetic acid leads to hydrogen abstraction by the carbonyl oxygen radical-cation fonning a carbon radical, then further oxidation of the radical to the carbocation and migration of this centre along the carbon chain by a series of hydride transfer steps. Long chain ketones yield a mixture of alcohol trifluoToacetates by reaction of the carbocation centres with the solvent [3]. 

Reaction between a long-chain ketone and a diol will lead to a surfactant that contains a ketal bond. The synthesis is analogous with those given in Figs. 13 and 14 for the preparation of acetal surfactants [52]. Ketal-based surfactants have also been prepared in good yields from esters of keto acids by either of two routes, as shown in Fig. 15 [53-55]. 

Note that in long-chain ketones the hydrocarbon peaks are indistinguishable (without the aid of high-resolution techniques) from the acyl peaks, since the mass of the C=0 unit (28) is the same as two methylene units. 

A general ketone synthesis has been developed involving reaction of trimethyl(perfluorooc-tyl)silane with acid fluorides. Yields, e.g. of 23 and 24, are generally good, and conversion of these ketones into tertiary alcohol derivatives tends to be slow, in part due to rather low solubility of the long-chain ketones.47 Indeed, it is somewhat surprising that these ketones do not react readily with trialkyl(perfluoroalkyl)silanes under these conditions to give tertiary alcohol derivatives.47... 

Paleotemperature might be reconstructed in ancient sediments through biomarker signals if cold-adapted and warm-adapted organisms produced distinctive lipids. The best-known example of such a signal is the long-chain ketones produced by haptophytes that carry patterns of unsaturation determined by sea-surface temperature (Brassell et al., 1986). 

For a number of cyclic or long-chain ketones, thionyl chloride in pyridine at 0°C proved to be the reagent of choice for effecting the dehydration, and gave 88 to 94% yield of alkenes (Table 12). ... 

The degree of unsaturation of long-chain ketones in Emiliania huxleyi can be evaluated from the concentrations of the dominant di- and triunsaturated C37 components (C37.2 and C37.3 respectively see Fig. 5.1) ... 

RechkaJ.A., MaxwellJ.R. (1988) Unusual long chain ketones of algal origin. Tetr. Letts 29, 2599—600. 

Reactions a and b occur with statistical probability giving long chain ketone and butyl ketone, which are observable in these experiments. Model compound measurements show that in the n-butyl ketone group, the butyl C2 carbon resonance moves from 23.4 to 22.7 ppm, coinciding with the C2 resonance of "amyl + long branches, the intensity of which increases upon oxidation. By comparing these results quantitatively with the overall production of oxidized structures, the reactivity ratio of branch points to linear chains is calculated to be 9.8 . 1.0. This result is in agreement with the value of 8 derived from model hydrocarbon oxidation studies (15). 

Asinger and his co-workers410 described the use of a cobalt catalyst for hydrogenation of long-chain ketones at about 200° and 200 atm. 

It was found from the analysis of laboratory cultures and field samples that the extent of unsaturation (number of double bonds) in these long-chain ketones varies linearly with growth temperature of the algae over a wide temperature range (Brassell et al. 1986 Prahl and Wakeham 1987). To describe this, an unsaturation index was suggested, which in its simplified form is defined by the concentration ratio of the two... 

Figure 6-1. Influence of goodness of solvent, as measured by the solubility parameter, 6i, of the solvent, on the intrinsic viscosity. [17], of dissolved natural rubber and on the volume fraction, 02, of the cross-linked natural rubber polymer in aliphatic hydrocarbons, (O), long-chain esters, ( ), and long-chain ketones, (O). After data from G. M. Bristow and W. F. Watson. The solubility parameter is given in the traditional physical units.

---