Tertiary thiols

Another method involves treatment with Lawesson s reagent (see 16-10). When epoxides are substrates, the products are 3-hydroxy thiols. Tertiary nitro compounds give thiols (RNO2 RSH) when treated with sulfur and sodium sulfide, followed by amalgamated aluminum. 

Hydroxyls primary and secondary amines thiols Tertiary amines... 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

Thiols can be prepared by a variety of methods. The most-utilised of these synthetic methods for tertiary and secondary thiols is acid-catalysed synthesis for normal and secondary thiols, the most-utilised methods are free-radical-initiated, alcohol substitution, or halide substitution for mercaptoalcohols, the most-utilised method is oxhane addition and for mercaptoacids and mercaptonitnles, the most-utilised methods are Michael-type additions. 

Oxidation. Disulfides are prepared commercially by two types of reactions. The first is an oxidation reaction uti1i2ing the thiol and a suitable oxidant as in equation 18 for 2,2,5,5-tetramethyl-3,4-dithiahexane. The most common oxidants are chlorine, oxygen (29), elemental sulfur, or hydrogen peroxide. Carbon tetrachloride (30) has also been used. This type of reaction is extremely exothermic. Some thiols, notably tertiary thiols and long-chain thiols, are resistant to oxidation, primarily because of steric hindrance or poor solubiUty of the oxidant in the thiol. This type of process is used in the preparation of symmetric disulfides, RSSR. The second type of reaction is the reaction of a sulfenyl haUde with a thiol (eq. 19). This process is used to prepare unsymmetric disulfides, RSSR such as 4,4-dimethyl-2,3-dithiahexane. Other methods may be found in the Hterature (28). 

Aliphatic Alcohols and Thiols. Ahphatic alcohols on reaction with chloroformates give carbonates and hydrogen chloride. Frequendy, the reaction proceeds at room temperature without a catalyst or hydrogen chloride acceptor. However, faster reactions and better yields are obtained in the presence of alkaU metals or their hydroxides, or tertiary amines. Reactions of chloroformates with thiols yield monothiolocarbonates (14). 

If tertiary chlorine atoms are indeed critical to heat resistance, then reactions that consume them should improve polymer stabiUty. This is indeed the case. Post-reaction of polychloroprene with dodecyl mercaptan (111), use of higher levels of ethylene thiourea for curing (112), and inclusion of reactive thiols such as mercaptobenzimidazole in cure systems (113) all improve heat resistance. This latter technique is especially effective in improving the heat resistance of mercaptan modified polychloroprene. 

TBDMSCl, imidazole, DMF, 25°, 10 h, high yields. This is the most common method for the introduction of the TBDMS group on alcohols with low steric demand. The method works best when the reactions are run in very concentrated solutions. This combination of reagents also silylates phenols, hydroperoxides," and hydroxylamines. Thiols, amines, and carboxylic acids are not effectively silylated under these conditions. Tertiary alcohols can be silylated with the phosphoramidate... 

Tertiary nitro compounds are converted into the cortespooding thiols by the reacdon with sodium sulfide and snlfnr fSj in DMSO followed by the redncdon with Al-Hg. fEq. 7.12. Secondary and primary nitro compounds do not give thiols in these reacdons instead, a complex set of product is formed. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions). The R group may be alkyl or aryl and organolithium bases can be used to deprotonate the thiol. As in 10-37, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson... 

Primary and secondary but not tertiary alkyl halides are easily converted to Bunte salts (RSSOj ) by treatment with thiosulfate ion. ° Bunte salts can be hydrolyzed with acids to give the corresponding thiols or converted to disulfides, tetrasulfides,... 

Gold nanoparticles stabilized by primary amine, tertiary amine, sulfide, and thiols... 

Scheme 2. Production of size-regulated gold nanoparticles stabilized by primary amines, tertiary amines, sulfides, and thiols formed by the controlled thermolysis of gold(I) thiolate complex in the presence of amine (reprinted from Ref. [11], 2005, with permission from Elsevier).

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

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