Thiopropionate esters

Another method for slowing oxidation of rubber adhesives is to add a compound which destroys the hydroperoxides formed in step 3, before they can decompose into radicals and start the degradation of new polymer chains. These materials are called hydroperoxide decomposers, preventive antioxidants or secondary antioxidants. Phosphites (phosphite esters, organophosphite chelators, dibasic lead phosphite) and sulphides (i.e. thiopropionate esters, metal dithiolates) are typical secondary antioxidants. Phosphite esters decompose hydroperoxides to yield phosphates and alcohols. Sulphur compounds, however, decompose hydroperoxides catalytically. 

Sulphur compounds, e.g., thiopropionate esters and metal dithiolates (Table la, AO 16 and 17), decompose hydroperoxides catalytically, i.e., one antioxidant molecule destroys several hydroperoxides through the intermediacy of sulphur acids [19,20]. Scheme 6 shows a simplified scheme for the antioxidant mechanism of simple alkyl sulphides. 

Esters of thiopropionic acid tend to decompose at high processing temperatures, and their odor makes them unsuitable for some food-packaging apphcations. 

Among the sulphur-containing substances, esters of 3,3 -thiopropionic acids S(CH2CH2COOR)2, where R=C 4—C20 [18], are most efficient. 

Simple alkyl or aryl thioesters are commonly assayed as substrates of hydrolases, witness the hydrolysis of phenyl thioesters by horse serum carbox-ylesterase [150], For most substrates investigated, e.g., phenyl thioacetate, phenyl thiopropionate, and phenyl thiobutyrate (7.66, R = Me, Et, and Bu, respectively), kcat values were found, which were a few times larger than those of corresponding nitrophenyl esters, whereas the affinities were lower by approximately one order of magnitude. Methyl and phenyl esters of various linear thioacids were also found to be good substrates of mammalian liver carboxylesterases and serum cholinesterases [151]. 

Unterwirft man den /3-Thiopropion-essigsaureester der Dieckmann-Kondensation, so entsteht als Hauptprodukt derThiophanon-(3)-carbon-saure-(2)-ester 98), (10), (56), (11) ... 

The Evans Cu(II)- and Sn(II)-catalyzed processes are unique in their ability to mediate aldol additions to pyruvate. Thus, the process provides convenient access to tertiary a-hydroxy esters, a class of chiral compounds not otherwise readily accessed with known methods in asymmetric catalysis. The process has been extended further to include a-dike-tone 101 (Eqs. 8B2.22 and 8B2.23). It is remarkable that the Cu(II) and Sn(II) complexes display enzyme-like group selectivity, as the complexes can differentiate between ethyl and methyl groups in the addition of thiopropionate-derived Z-silyl ketene acetal to 101. As discussed above, either syn or anti diastereomers may be prepared by selection of the Cu(II) or Sn(II) catalyst, respectively. 

The elimination/addition reaction already proceeded at room temperature when the dichloropropionic acid had been linked as an ester to the support, but required heating when an amide linkage had been chosen. When amines with low nucleophilicity were used, such as aniline or a-amino acid esters, higher reaction temperatures were also beneficial. Occasional by-products for this reaction sequence were acrylic acid derivatives or the corresponding hydrogenated products (2-thiopropionic acid derivatives). These by-products were usually formed when a very small excess of amine was used in the elimination/addition step. Both the thiols and the amines used in this reaction sequence could be polyfunctional, as illustrated by the examples sketched in Fig. 3. 

Asymmetric Aldol Reactions. Reaction of (1) with Boron Tribromide in CH2CI2 affords, after removal of solvent and HBr, a complex (5) useful for the preparation of chiral enolates (eq 5). Complex (5) is moisture sensitive and is generally prepared immediately before use. For propionate derivatives, either syn or, less selectively, anti aldol adducts may be obtained by selection of the appropriate ester derivative and conditions. Thus reaction of f-butyl propionate with (5) and triethylamine produces the corresponding E 0) enolate, leading to formation of anti aldol adducts upon addition to an aldehyde (eq 6). Selectivities may be enhanced by substitution of the t-butyl ester with the (+)-menthyl ester. Conversely, reaction of 5-phenyl thiopropionate with (5) and Diisopropylethylamine affords the corresponding Z(0) enolates and syn aldol products (eq 7). ... 

Synonyms Dioctadecyl thiodipropionate 3,3-Dioctadecyl thiodipropionate Di-n-octadecyl 3,3-thiodipropionate Disteaiyl 3,3-thiodipropionate Distearyl 3-thiodipropionate Disteaiyl f3,f3-thiodipropionate Disteaiyl thiopropionate DSTDP DSTP Propanoic acid, 3,3-thiobis-, dioctadecyl ester Propionic acid, 3,3-thiobis-, dioctadecyl ester 3,3-Thiobispropanoic acid, dioctadecyl ester Thiodipropionic acid, disteaiyl ester... 

It is important to recognize that additives suitable for one type of resin may have detrimental effects on another and/or on their additives. Furthermore, the stabilizing systems of one polymer type may neutralize the system of another polymer. For example, to stabilize postconsumer waste (PCW), 55-75 wt% PO, 5-25 wt% PS, 5-15 wt% PVC, and 0-10 wt% other thermoplastics, 0.1-0.5 wt% of a stabilizer mixture was added. The mixture comprised a sterically hindered phenol [pentaerythritol ester] and tris(2,4-di-tert-butylphenyl) phosphite at a ratio of 5 1-1 5. For other compositions of PCW, different stabilizers, viz., thiopropionic acid, benzophenones, oxalides, benzotriazoles, HALS, and/or CaO, may have to be used (Pauquet et al. 1994). 

Common stabilizers for organic cellulose molding compounds include epoxides, especially epoxidized soybean oil, alkaline and alkaline-earth salts of acetic and carbonic acid as well as tartaric acid, oxalic acid and citric acid. Effective antioxidants include substituted phenols, such as t-butylphenol, or preferably sterically hindered phenols, such as 2,6-di-tert-butyl-p-cresol. Diphenylamine or esters of thiopropionic acid exhibit an effect similar to that of antioxidants [501]. 

Whereas carboxylic esters had been considered to be inert under the conditions of boron enolate formation by enolization [2c], Corey s group elaborated protocols that allowed for the generation of boron enolates from esters. Thus, trans-boron enolates 100 result from simple carboxylic esters by deprotonation, while 5-phenyl thiopropionate formed cis-enolate 101 - in accordance with Masamune s observation. In both cases, the C2-symmetric diazaborolidine 99 served as the Lewis acid for enolization (Scheme 2.28) [112]. The stereochemical divergence of ester and thioester has been rationalized by postulating an E2-type elimination mechanism starting from the complex 102 that loses bromide in a... 

The combined introduction of an inhibitor, which terminates chains, and a substance, which decomposes hydroperoxides, is widely used for the more efficient retardation of oxidation processes in polyolefins, resins, lubricants, and other materials. Various phenols, bisphenols, and aromatic amines are applied as an acceptor of RO 2, and aryl phosphites, esters of thiopropionic acid, dialkyl dithiopropionates and thiophosphates of zinc and nickel, and other similar compounds are introduced to... 

The tropical category is one of the most important areas for new discoveries of key impact flavor compounds. Analyses of passion fruit and durian flavors have produced identifications of many potent sulfur aroma compounds (18). Among these is fropathiane, 2-methyl-4-propyl-l,3-oxathiane, which has an odor threshold of 3 ppb (15). For pineapple, 2-propenyl hexanoate (allyl caproate) exhibits a typical pineapple character (11) however, Furaneol, ethyl 3-methyl-thiopropionate, and ethyl-2-methylbutyrate are important supporting character impact compounds (31). The latter ester contributes the background apple note to pineapple flavor. Another character impact compound, allyl 3-cyclohexyl-... 

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