3- Mercapto-2-pentanone

The cyclization of a-mercaptoketones with ammonium thiocyanate leads to the corresponding 2-mercaptothiazoles (144). For example, 2-mercapto-3-pentanone in ethereal solution with sulfuric acid gives 4-ethyl-5-methyl-2-mercaptothiazole (10), Ri = SH, R2 = Et, R3 = Me, when allowed to stand for 3 hr without heating with ammonium thiocyanate. 

Kerscher, R., Grosch, W. (1998) Quantification of 2-methyl-3-furanthiol, 2-furfurylthiol, 3-mer-capto-2-pentanone, and 2-mercapto-3-pentanone in heated meat. J. Agric. Food Chem. 46, 1954-1958... 

Cyclohexylthio)-3-pentanone This sulfide was obtained by heating 2-mercapto-3-pentanone (0.5 mole), freshly distilled cyclohexene (0.5 mole), and benzoyl peroxide (400 mg) under reflux for 8 h and then fractionating the mixture in a vacuum. The product has b.p. 89°/2 mm, the yield being 44%. 

Mercapto-3-pentanone and other thiols have also been added to styrene, 2-methyl-2-butene, 1-methyl-1-cyclohexene, and olefins containing functional groups38 such as vinyl chloride, 1-chlorocyclohexene, 2-chlorocrotonaldehyde, allylamine, allyl alcohol, bromide and chloride, and cinnamyl alcohol. 

Thiazolines 58 One mole each of an aldimine and 2-mercapto-3-pentanone are boiled in benzene (300 ml) under a Dean and Stark apparatus until no more water appears in the separator. Then the solvent is evaporated and the residue is distilled in a vacuum or recrystallized. The 4-thiazolines recorded in the Table below were prepared by this method. 

The reaction can be extended to other mercapto derivatives such as a-mercapto ketones474 and a-mercapto carboxylic acids.475 For example, 3-ethyl-5,6-di-hydro-2-methyl-4i/-1,4-thiazine is obtained in 85-90% yield from aziridine and 2-mercapto-3-pentanone 474... 

Table 11.19. Concentrations (/ig per kg) of 2-methyl-3-furanthiol (MFT), 2-furfurylthiol (FFT), 3-mercapto-2-pentanone (3M2P), and 2-mercapto-3-pentanone (2M3P) in cooked meat ...

Bis-(3-pentanon-2-yl) disulfide added dropwise with stirring during 2 hrs. at 100° in a slow Ng-stream to a mixture of 3.3 N NaOH and o-phenylenediamine, heating continued 5 hrs. at the same temp. 2-methyl-3-ethylquinoxaline (Y 93%) and 2-mercapto-3-pentanone (Y 41%).—The resulting sensitive a-diketones are isolated as quinoxalines. F. e. s. F. Asinger, M. Thiel, and W. Schafer, A. 637, 146 (1960). 

Phenyl isothiocyanate and anhydrous K-carbonate in benzene ice-salt-cooled and treated with 2-mercapto-3-pentanone, more benzene added, and heated to reflux N-phenyl-S-(3-oxo-2-pentyl) dithiourethan (Y 87%) refluxed 3 hrs. with anhydrous ZnGl2 in abs. methanol 3-phenyl-4-ethyl-5-methyl-4-thiazo-line-2-thione (Y 90%). F. e., also 4-thiazolin-2-ones from isocyanates via thio-uretbans and without isolation of the intermediates (cf. Synth. Meth. lA, 655), s. K. Riihlmann, A. GrosaJski, and U. Schrapler, J. pr. 11, 54 (1960). 

H2SO4 in ether added dropwise with stirring and ice-salt-cooling to a mixture of 2-mercapto-3-pentanone and NH4-thiocyanate, the product isolated after 3 hrs. 2-mercapto-4-ethyl-5-methylthiazole. Y 88%. K. Riihlmann, A. Gro-salski, and U. Schrapler, J. pr. 11, 54 (1960). 

An equimolar mixture of 2-mercapto-3-pentanone and 1-amino-l-buten-3-one stirred whereupon after ca. 10 min. tbe temp, rises to 50-60°, tbe product isolated when tbe exothermic reaction has ceased and the mixture regained room temp. 5-methyl-4-ethyl-2-acetonyl-Zl -thiazoline (Y 78%) heated to 180° with distillation of the products 5-methyl-4-ethylthiazole (Y 92%). F. e. s. F. Asinger, L. Schroder, and S. Hoffmann, A. 64S, S3 (1961). 

An example for stimulus generalization are responses of rats to stress-inducing odors. Laboratoiy rats of the Wistar strain respond to predator odors, specifically mercapto compounds in fox droppings, with stress reactions, for example avoidance behavior such as freezing and increased plasma corticosterone concentrations (Vemet-Mauiy et ah, 1984). The rats were trained to avoid water scented with a mercapto odorant that contained both a keto- and a sulfhydryl group (4-mercapto-4-methyl-2-pentanone). As the animals licked a waterspout, a mild electric shock was applied to their tongue. When different compounds were tested thereafter, the rats avoided compounds with similar... 

At a silver reclamation facility in Duval County, Florida, a Biocube bioflltration system used to treat vapors containing mercaptans (mainly 4-mercapto-4-methyl-2-pentanone) cost 18,000 (D13551D). 

Biocube (T0039) is a commercially available off-gas treatment system. A Biocnbe was installed at a domestic wastewater pumping facility in June 1995 at a cost of 15,000. The pumping facility treats approximately 200 m of water per day (50,000 gal per day) (D13550C, pp. 1-4). At a silver reclamation facility in Duval County, Florida, a Biocube biofiltration system used to treat vapors containing mercaptans (mainly 4-mercapto-4-methyl-2-pentanone) cost 18,000 (D13551D). 

In the case of boiled beef the results of AEDA were compared with those of AECA. Table 16.4 indicates that they agreed except in three cases. The odour potencies of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 3-mercapto-2-pentanone and methional were more than one dilution step higher in AECA than in AEDA [56]. Most likely, portions of these odorants had been lost during concentration of the extract for AEDA. AECA was also used in studies on the aroma of pepper [55], coffee [57] and Camembert cheese [58]. 

Mercapto-4-methyl-2-pentanone CH3C(SHXCH3)CH2COCH3... 

T = 0.0004 jUg L ) and 3-mercapto-2-pentanone. The methylfuran moiety of 2-methyl-3-(methylthio)furan also originates in the ribose, but the methylthio carbon comes partly from ribose and partly from cysteine. All the carbons of 3-mercapto-... 

To explain the formation of 3-mercapto-2-pentanone without its 2,3-isomer, a new pathway was proposed (Scheme 5.15), in which 1,4-dideoxyosone and 5-hydroxy-3-mercapto-3-penten-2-one are intermediates. Both 2-methyl-3-furanthiol and 2-methyl-3-hydroxyfuran are readily derived from this pathway without involving norfuraneol. 

Scheme 5.15 Proposed formation of 3-mercapto-2-pentanone and 2-methyl-3-furanthiol from ribose and cysteine via l,4-dideoxy-2,3-diketose2X...

Fig. 3.23 Formation of 2-furfurylthiol, 2-methyl-3-furathiol, 3-mercapto-2-pentanone and 3-mercato-2-butanone from pentose and cysteine...

Van der Linde and co-workers [71] postulated 5-hydroxy-3-mercapto-2-pentanone (44) as key intermediate, formed by hydrolysis of 43 (cf. Fig. 3.30). Another postulated intermediate, 3,5-dihydroxypentan-2-one [70], however, generated only trace amounts of 13, when reacted with cysteine or hydrogen sulphide [72[. 

Among the major volatile sulfur compounds generated during the preparation of die ketopentose-L-cysteines are 2-methylfuran-3-thiol, 2-furfurylthiol and 3-mercapto-2-pentanone (13, Table I). These compoimds have also been identified as character impact compounds of boiled meat flavor (II, 12). This suggests that ketopentosese-L-cysteines are playing a role in the development of boiled meat flavor. Ketohexose-L-cysteines do not produce these character impact compounds in significant quantities (Table I) and are therefore unlikely to play a role in boiled meat flavor development. 

As for the potent odorants in green tea (sen-cha) drinks, the eleven components shown in hgure 17.7 are found to be important contributors to its characteristics. Using the AEDA method, the characteristic sulfur components, such as 4-methoxy-2-methyl-2-butanethiol, 4-mercapto-4-methyl-2-pentanone, and methional, were identihed from the green tea for the first time. Among these eleven components, P-damascenone and methional were reported to increase after the heating process (hgure 17.4), then theorized to have a remarkable effect on the tea drink quality. 

Acetyl-1-pyrroline 4-Mercapto-4-methyl-2-pentanone 2-Ethyl-3,5-dimethylpyrazine (Popcorn-like) (Meaty) (Nutty)... 

FIGURE 17.16 Proposed precursor flavor components of 2-acetyl-l-pyrroline, 4-mercapto-4-methyl-2-pentanone, 2-acetyl-l-thiazoline, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone. 

Kumazawa, K., Kubota, K., and Masuda, H. 2005. Influence of manufacturing conditions and crop season on the formation of 4-mercapto-4-methyl-2-pentanone in Japanese green tea (sen-cha). J. Agric. Food Chem. 53 5390-96. 

However, the addition occurs contrary to the Markovnikov rule under irradiation by ultraviolet light or in the presence of peroxides 1 for instance, allyl-amine hydrochloride or a derivative thereof in alcoholic solution is thiolated by an excess of hydrogen sulfide under UV-irradiation, exclusively (yields up to 57%), to give 3-aminoalkanethiols.2 Addition of hydrogen sulfide is of use in the laboratory only when the reaction can be carried out in the liquid phase and is then preferably effected under the influence of a basic catalyst Dahl-bom,3 for instance, obtained 3-mefcapto-butyric acid from crotonic acid hydrogen sulfide in the presence of diethylamine in a closed vessel at 70° and 4-mercapto-4-methyl-2-pentanone is obtained in 80% yield from mesityl oxide and hydrogen sulfide with triethylamine as catalyst.4... 

---