Hydrolysis s. a. Cleavage

Hydrohalogenation s. Halides from ethylene derivs. Hydrolysis (s. a. Cleavage,... 

Hydrolysis of dialkyl sulfites under acidic and alkaline conditions, which is followed by the use of OH2, proceeds by attack at sulfur to give S—O cleavage (72). The rate of hydrolysis is generally faster for cycHc and aryl sulfites than for dialkyl sulfites (73). Activation parameters of hydrolysis are known for some sulfites, and the increased rate for ethylene sulfite results from a reduced entropy of activation which results from a rigid ring stmcture (74). 

Sodium ethyl thiosulfate [26264-37-9] is also known as Bunte s salt after the name of its discoverer. Bunte salts may be thought of as esters of thiosulfuric acid (94—96). In essentially all of their chemical reactions, the cleavage is between the divalent and hexavalent sulfur atom. For example, acid hydrolysis produces a thiol and the acid sulfate ... 

Fig. 3.6. Stereoelectronic control of the cleavage of the tetrahedral intermediate during hydrolysis of a peptide bond by a serine hydrolase. The thin lines represent the reactive groups of the enzyme (serine, imidazole ring of histidine) the thick lines represent the tetrahedral intermediate of the transition state. The full circles are O-atoms open circles are N-atoms. The dotted lines represent H-bonds the thick double arrow indicates an unfavorable dipole-dipole interaction [21]. A (R)-configured N-center B (S)-configured N-center.

Heterolytic scission of the -S-S- bond in which only electrophilic assistance is involved is the exception rather than the rule in reactions involving bond fission of this type. Kice et a/.165,166 have demonstrated that a variety of S-S bond cleavages involve concomitant electrophilic and nucleophilic catalysis including (a) the formation of aryl thiolsulfones from aryl thiolsulfinates and aryl sulfinic acids and (b) the hydrolysis (acetic acid—1% water and 60%... 

The thionation of 2-substituted-4-aryl-5,5-dimethyl-l,3,2-dioxaphosphorinanones with Lawessen s reagent proceeded predominantly with retention of configuration and a cyclic pentacoordinated intermediate was proposed.248 Both P—N bond cleavage in acidic solution and P—C and P—O bond cleavage in basic solution occur in the hydrolysis of A-(methoxycarbonyl)carbamoylmcthoxyphosphonyl)-a-amino acid ester. Only P—O bond cleavage occurs with the ATisopropy Icarbamoy I) compound.249... 

Ab initio calculations have been earned out on the gas-phase acid-catalysed hydrolysis reactions of sulfinamide (319) using the 3-21G sets.290 The first step in the acid-catalysed hydrolysis of A-methylmethanesulfinamide (319 R1 = R2 = Me) is O-protonation and this form is then transformed by addition of water to the sulfiirane intermediate (320). Intramolecular proton transfer from 0 to N follows and then slow N—S bond cleavage to give products.290 Studies with (319 R1 = Me, R2 =aryl) also... 

The hydrolysis of a series of spiro-/4-sulfanes such as (330)-(332) leads to sulfoxides in dioxane-water solutions. A mechanism involving slow nucleophilic attack of water on the positively polarized sulfur atom and simultaneous 0—H and S—N bond cleavage is proposed.298 The photo-oxidation of the sulfenamides (333 R = Me, Et, Ph, Bn, etc.) has been reported.299... 

Theoretical studies of the hydrolysis of lV-benzyl-3-oxo-/5-sultam (115) showed that the activation energies for the pathways leading to the products of C-N and S-N cleavage for the uncatalysed hydrolysis were very similar. However, when a second water molecule was involved, cleavage of the C-N bond was preferred.115 In a review, the mechanisms of reactions of /5-sultams have been compared with those of /3-lactams, including their reactions with some serine enzymes.91... 

In a theoretical study of the alkaline hydrolysis of 0,5-dimethyl methylphospho-nothiolate, it was found that the P-O and P-S bond cleavage processes were kinetically competitive but that the products of P-S bond cleavage were thermodynamically favoured.104... 

Some tricyclic 1,3-thiazetidines of type (51) are reported (95CPB63). Selective C-S bond cleavage of 3-aryl-fS-sultams (52) with ethylaluminium dichloride gives aryl ketones or aldehydes by a process involving 1,2-aryl shift, imine formation and hydrolysis of the imine (95TL245). 

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