Dipropyl disulfide

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

In the case of PCSO the addition of N20 leads to increased formation of cysteic acid, alanine and dipropyl sulfide and to a decrease in the yield of dipropyl disulfide. The addition of KBr decreases the yield of all the four products. These findings indicate that cysteic acid and alanine are formed by the reaction of OH radicals in parallel reactions as given in Figure 7. 

The authors suggested that di-n-propyl disulfide is formed by the reaction of both hydrated electrons and OH radicals, however it should be mentioned that the yield from hydrated electrons should be higher than from OH radicals as otherwise N20 will not reduce the yield of dipropyl disulfide as N20 merely converts eaq to OH radicals. The yield from each radical could be calculated from the yields in the presence of the various scavengers, but unfortunately these data were not given by the authors. 

An example of a larval parasitoid that responds to the host sex pheromone is seen with Cotesiaplutellae (Braconidae), also a parasitoid of the diamondback moth. These insects were attracted equally to the pheromone blend (31,32,33, see above), the acetate 32, or aldehyde 31 components [80]. This larval parasitoid, however, was also strongly attracted to host frass volatiles, in particular, dipropyl disulfide 34, dimethyl disulfide 35, allyl isothiocyanate 36, and dimethyl trisulfide 37. In contrast, the egg parasitoid Trichogramma chilonis was only weakly attracted to 36. In both, T. chilonis and C. plutellae, plant volatiles, in particular (3Z)-hex-3-en-l-yl acetate 38, significantly enhanced attraction by the pheromone [80]. 

Host frass volatiles [attraction] Dipropyl disulfide 34, dimethyl disulfide 35, allyl isothiocyanate 36 dimethyl trisulfide 37 [80]... 

Aliphatic sulfur compounds, in particular disulfides such as methyl propyl disulfide, dipropyl disulfide, and especially cis- and /ran -propenyl propenyl disulfide are mainly responsible for the typical odor of onion oil [235]. The presence of 2-hexyl-5-methyl-3(2H)-furanone [33922-66-6] is a characteristic of authenticity [235a]. 

The most important flavour compound in raw onions is thiopropanal-S-ox-ide, the lachrymatory factor [145,146]. Other important flavour compounds are 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene and alkyl alkane thiosulfonates such as propyl methanethiosulfonate and propyl propanethiosulfonate with a distinct odour of freshly cut onions [35, 36, 147]. Various thiosulfinates that have a sharp and pungent odour may also contribute to the flavour of onions. These compounds, however, are rapidly decomposed to a mixture of alkyl and alkenyl monosulfides, disulfides and trisulfides (Scheme 7.3) of which dipropyl disulfide, methyl ( )-propenyl disulfide, propyl ( )-propenyl disulfide, dipropyl trisulfide and methyl propyl trisulfide are the most important contributors to the aroma of raw and cooked onions (Table 7.5, Fig. 7.6) [148-150]. Recently, 3-mercapto-2-methylpentan-l-ol was identified in raw and cooked onions eliciting intense meat broth, sweaty, onion and leek-like odours [142, 151]. 

Shallots Allium ascalonicum) are an allium wherein the bulb laterals separate into individual bulbs. Apparently, shallots do not develop a lachrymatory factor, such as thiopropanal-S-oxide upon maceration [35]. The major aroma constituents in shallots are similar to those found in A.cepa. In raw shallots, the most important aroma compounds appear to be dipropyl disulfide, propyl ( )-prope-nyl disulfide, methyl propyl trisulfide, dimethyl trisulfide and dipropyl trisulfide (Table 7.5, Fig. 7.6) [35, 152, 153]. 

The l3C CP MAS spectra of the sample-A show the presence of the most prominent peak at 27.2 ppm for Ci carbon atom adjacent to the SH group and C2 carbon atom of the 3-mercaptopropyl group. There was another minor intensity broad peak at around 22.3 ppm which is assigned to C and C2 carbon atoms of the dipropyl disulfide. The presence of dipropyl disulfide in the sample A may be due to oxidative dehydrogenation of two adjacent thiol groups leading to the formation of disulfide (S-S) group. An unresolved shoulder down field to the C3 carbon of the thiol was observed for the C3 carbon of the dipropyl disulfide. Similar results were obtained by Lim et al. [6],... 

Another German investigator (Semmler, 1892) also produced garlic oil via steam distillation. The oil yielded diallvl disulfide, CH2=CHCH2SSCH2 CH = CH2, with minor amounts of diallyl trisulfide and diallyl tetrasulfide present. The oil yielded by similar experimentation with onions was different, containing essentially propionaldehyde, C2H5CHO, plus a number of sulfur compounds, of which dipropyl disulfide, C5H12S2, was one. 

Onion (raw) Allium cepa trisulfide Propanethial S-oxide (153), dipropyl disulfide (154), 131,170,171,172... 

Alkyl sulfides and thiols. Some alkyl thiols and sulfides, notably those from commonly ingested Allium sativum (garlic) and Allium cepa (onion) (Alliaceae), are variously bioactive as odorants and antimicrobials. Propanethial S-oxide (CH3-CH2-CH=S=0) is a lachrymatory irritant principle of onion. Allicin (S-oxodiallydisulfide CH2=CH—CH2-SO-S-CH2— CH=CH2), diallyldisulfide (CH2=CH-CH2-S-S-CH2-CH=CH2) and diallylsulfide (CH2=CH—CH2—S—CH2-CH=CH2) are major odorants of garlic that are reactive and irritant because of the allyl groups. Dimethyl disulfide (CH3—S—S-CH3), dipropyl disulfide (CH3-CH2-CH2-S-S-CH2-CH2-CH3), methyl allyl disulfide (CH3-S-S-CH2-CH=CH2) and propane-1-thiol (CH3-CH2—CH2—SH) are further Allium odorants. Methane thiol (methyl mercaptan CH3—SH) is a widespread plant volatile and notably derives from anaerobic bacterial degradation of cysteine as in human flatus and bad mouth odour. The aliphatic disulfides allicin and ajoene inhibit proinflammatory expression of iNOS. 

C6H14S2 dipropyl disulfide 629-19-6 -85.48 1.2250 2 9504 C7H3CIF202 2-chloro-4,5-difluorobenzoic acid 110877-64-0 25.00 1.4821 2... 

C6H140 ethyl isobutyl ether 627-02-1 164.11 8.961 2 9130 C6H14S2 dipropyl disulfide 629-19-6 187.68 13.810 1... 

C6H1005 dilactic acid 19201-34-4 1.210E+10 84.080 9130 C6H14S2 dipropyl disulfide 629-19-6. 224E+ 0 90.960... 

C6H14S2 dipropyl disulfide 629-19-6 in benzene 1.979 1 11537 C7H1204 heptanedioic acid 111-16-0 in dioxane 2.389 1... 

H5PV2Mo10O40 Acetaldehyde 1 -propanethiol THTb Acetic acid dipropyl disulfide THTCr... 

Recoveries also depend on the wine matrix white and red wines differ for volatiles and polyphenols, and contents of alcohol and sugars. For quantitative analysis, internal standards have to be spiked to the sample in suitable concentration, such as dimethyl sulfide-d6 (d6-DMS) 25 pg/L, dipropyl disulfide (DPDS) 25 pg/L, 4-methylthiazole (MT) lOpg/L, and 3-(methylthio)-l-hexanol (MTH) 50pg/L. A white wine matrix can be used [e.g., 10% v/v ethanol, sugar content <4g/L, and a polyphenolic content of 115mg/L expressed as (+)-catechin] for preparation of standard solutions to calculate the calibration curve for analytes, containing total S02 corrected to 100 g/L and previously treated twice with charcoal 3 g/L to remove sulfur and less polar volatile compounds (higher alcohols are not removed). 

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