Salt cleaving

In 1928, Malaprade discovered that periodic acid and its salts cleaved the carbon-carbon bond of... 

A modification of this general procedure was used in the synthesis of (prop-2-enylidene)cyclo-propane (allylidenecyclopropane, 12).Allyl bromide was first alkylated in 81 -90% yield with l-lithio-l-(phenylsulfanyl)cyclopropane (10) in the presence of copper(I) iodide or cop-per(I) iodide-dimethyl sulfide. The adduct was then methylated with methyl fluorosulfonate or with dimethyl sulfate, and the sulfonium salt cleaved with powdered potassium hydroxide in dimethyl sulfoxide, to give the product in 50-70% overall yield for the second step. 

Reduction of diaryliodonium cations in dimethylformamide exhibits four waves. Contrary to observations in aqueous solution, under these conditions the potential of the first wave is counterion dependent for diaryliodonium halides [54], The first wave (la, —0.39 to —0.49 V versus SCE) is assigned to the reduction of phenylmercuric halide, formed by reaction of diphenyliodo-nium halide with mercury electrode. In agreement with Beringer s results in water, the second wave (lb, —0.57 V versus SCE) is associated with reduction of solution-soluble diphenyliodonium cation at an electrode surface saturated with phenylmercury radical from wave la. The third wave (II, —1.70 V versus SCE) corresponds to two-electron reduction of iodobenzene to benzene, while the fourth wave (III, —1.95 V versus SCE) is due to one-electron reduction of phenylmercury radical [54], Unsymmetrical diaryliodonium salts cleave the aryl-iodine bond corresponding to the more electron deficient aryl group [58]. 

Analogously, copper(I) salts cleave diboron compounds [e.g., bis(pinacolato)diboron] to give, in the presence of an a,/3-enone, the corresponding conjugate boration product (eq 113). In contrast to the silylation procedure, reactions can be run at room temperature both on cyclic and acyclic enones. Subsequent oxidation of the borylated ketone provides the /3-hydroxyketone. 

Methyl ketones are cleaved on re action with excess halogen in the presence of base The products are a trihalomethane (haloform) and a carboxylate salt... 

Aqueous mineral acids react with BF to yield the hydrates of BF or the hydroxyfluoroboric acids, fluoroboric acid, or boric acid. Solution in aqueous alkali gives the soluble salts of the hydroxyfluoroboric acids, fluoroboric acids, or boric acid. Boron trifluoride, slightly soluble in many organic solvents including saturated hydrocarbons (qv), halogenated hydrocarbons, and aromatic compounds, easily polymerizes unsaturated compounds such as butylenes (qv), styrene (qv), or vinyl esters, as well as easily cleaved cycHc molecules such as tetrahydrofuran (see Furan derivatives). Other molecules containing electron-donating atoms such as O, S, N, P, etc, eg, alcohols, acids, amines, phosphines, and ethers, may dissolve BF to produce soluble adducts. 

Lewis acids, such as the haUde salts of the alkaline-earth metals, Cu(I), Cu(II), 2inc, Fe(III), aluminum, etc, are effective catalysts for this reaction (63). The ammonolysis of polyamides obtained from post-consumer waste has been used to cleave the polymer chain as the first step in a recycle process in which mixtures of nylon-6,6 and nylon-6 can be reconverted to diamine (64). The advantage of this approach Hes in the fact that both the adipamide [628-94-4] and 6-aminohexanoamide can be converted to hexarnethylenediarnine via their respective nitriles in a conventional two-step process in the presence of the diamine formed in the original ammonolysis reaction, thus avoiding a difficult and cosdy separation process. In addition, the mixture of nylon-6,6 and nylon-6 appears to react faster than does either polyamide alone. 

Whereas metal salts of carboxyUc acids cataly2e the above reactions, these are not sufftciendy basic to cleave Si—H bonds. Mercury salts of organic acids in the presence of silver perchlorate, however, do react to produce organoacyloxysdanes (111). 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

The initial sulfur copolymer that is formed is often high conversion and gelled. Molecular weight is reduced to the required level by cleaving some of the polysulfide Linkages, usually with tetraethylthiuram disulfide. An alkaU metal or ammonium salt (30) of the dithiocarbamate, an alkaU metal salt of mercaptobensothiasole (31), and a secondary amine (32) have all been used as catalysts. The peptization reaction results in reactive chain ends. Polymer peptized with diphenyl tetrasulfide was reported to have improved viscosity stabiUty (33). 

Thus quaternized thiazoles (170) consume two equivalents of OH on titration because the pseudo bases (171) ring open to (172), which form anions (173). Quaternized oxazoles (174) are readily attacked by hydroxide to give open-chain products such as (175) (74AHC(17)99), and quaternized 1,3,4-oxadiazoles behave similarly. Quaternary isothiazoles (e.g. 176) are cleaved by hydroxide (72AHC(l4)l), as are 1,2,4-thiadiazolium salts (177 178). 

Anthranils are readily cleaved by nitrous acid, presumably by attack of water on (V- nitroso cations. The first product that can be observed is the nitrosohydroxylamino compound (179), which becomes reduced to the diazonium salt (180) (67AHC(8)277). 

Anthiylmethyl ethers, formed from the sodium salt of a phenol and 9-anthryl-methyl chloride in DMF, can be cleaved with CH3SNa (DMF, 25°, 20 min, 85-99% yield). They are also cleaved by CF3CO2H/CH2CI2 (0°, 10 min, 100% yield) they are stable to CF3C02H/dioxane (25°, 1 h). ... 

A carbonyl group can be protected as a sulfur derivative—for example, a dithio acetal or ketal, 1,3-dithiane, or 1,3-dithiolane—by reaction of the carbonyl compound in the presence of an acid catalyst with a thiol or dithiol. The derivatives are in general cleaved by reaction with Hg(II) salts or oxidation acidic hydrolysis is unsatisfactory. The acyclic derivatives are formed and hydrolyzed much more readily than their cyclic counterparts. Representative examples of formation and cleavage are shown below. 

Attempted cleavage using Hg(II) salts gave material that could not be distilled. 1,3-Dithiolanes can also be cleaved with Ag20 (MeOH, H2O, reflux, 16 h-4 days, 75-85% yield). 

Acyclic monothio acetals and ketals can be prepared directly from a carbonyl compound or by transketalization, a reaction that does not involve a free carbonyl group, from a 1,3-dithiane or 1,3-dithiolane. They are cleaved by acidic hydrolysis or Hg(II) salts. 

The carboxamidomethyl ester was prepared for use in peptide synthesis. It is formed from the cesium salt of an A-protected amino acid and a-chloroacetamide (60-85% yield). It is cleaved with 0.5 M NaOH or NaHCOa in DMF/H2O. It is stable to the conditions required to remove BOC, Cbz, Fmoc, and r-butyl esters. It cannot be selectively cleaved in the presence of a benzyl ester of aspartic acid. ... 

The Tcrom ester is prepared from the cesium salt of an N-protected amino acid by reaction with 2-(trifluoromethyl)-6-chromylmethyl bromide (DMF, 25°, 4 h, 53-89% yield). Cleavage of the Tcrom group is effected by brief treatment with n-propylamine (2 min, 25°, 96% yield). It is stable to HCl/dioxane, used to cleave a BOC group. ... 

Sulfobenzyl esters were prepared (cesium salt or dicyclohexylammonium salt, Na03SC6H4CH2Br, DMF, 37-95% yield) from A -protected amino acids. They are cleaved by hydrogenolysis (H2/Pd), or hydrolysis (NaOH, dioxane/water). Treatment with ammonia-or hydrazine results in formation of the amide or hydrazide. The ester is stable to 2 M HBr/AcOH and to CF3SO3H in CF3CO2H. The relative rates of hydrolysis and hydrazinolysis for different esters are as follows ... 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

Benzamidomethyl-A -methylcysteine has been prepared as a crystalline derivative (H0CH2NHC0C6H 5, anhydr. CF3CO2H, 25°, 45 min, 88% yield as the tri-fluoroacetate salt) and cleaved (100% yield) by treatment with mercury(II) acetate (pH 4, 25°, 1 h) followed by hydrogen sulfide. Attempted preparation of S-acetamidomethyl-N-methylcysteine resulted in noncrystalline material, shown by TLC to be a mixture. ... 

The benzylsulfonium salt is cleaved by hydrogenolysis (H2/Pd-C, MeOH) the 4-methoxybenzylsulfonium salt is cleaved by methylamine (100%). ... 

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