Isomerizations hydrate isomerism

Isomerism in the Metal-ammines.—Werner claimed for the coordination theory that in certain cases isomerism should occur, that isomerism being brought about by different causes. lie divided isomerism in the ammines into five groups, namely, structure isomerism, ionisation isomerism, hydrate isomerism, polymerism, and stereoisomerism. 

Isomerism in Metal-Ammines—Structure Isomerism—Ionisation Isomerism— Hydrate Isomerism—Polymerism—Stereo-isomerism. 

Ionization isomerism Hydration isomerism Coordination isomerism Linkage isomerism Polymerization isomerism... 

In fact, Werner played such a central and almost monopolistic role in coordination chemistry that his name is virtually synonymous with the field. Even today, almost 75 years after his death in 1919, coordination compounds, particularly metal-ammines, are still colloquially called Werner complexes. The coordination theory not only provided a logical explanation for known "molecular compounds, but also predicted series of unknown compounds, whose eventual discovery lent further weight to Werner s controversial ideas. He showed how ammonia could be replaced by water or other groups, and he demonstrated the existence of transition series between ammines, double salts, and hydrates. Werner recognized and named many types of inorganic isomerism such as coordination isomerism, polymerization isomerism, ionization isomerism, hydrate isomerism, salt isomerism, coordination position isomerism, and valence isomerism. He also postulated explanations for polynuclear complexes, hydrated metal ions, hydrolysis, and acids and bases. His view of the two types of chemical... 

Although 2 methylpropene undergoes acid catalyzed hydration m dilute sulfuric acid to form tert butyl alcohol (Section 6 10) a different reaction occurs m more concentrated solutions of sulfuric acid Rather than form the expected alkyl hydrogen sulfate (see Sec tion 6 9) 2 methylpropene is converted to a mixture of two isomeric C Hig alkenes... 

By analogy to the hydration of alkenes hydration of an alkyne is expected to yield an alcohol The kind of alcohol however would be of a special kind one m which the hydroxyl group is a substituent on a carbon-carbon double bond This type of alcohol IS called an enol (the double bond suffix ene plus the alcohol suffix ol) An important property of enols is their rapid isomerization to aldehydes or ketones under the condi tions of their formation... 

Acid catalyzed hydration (Section 9 12) Water adds to the triple bond of alkynes to yield ketones by way of an unstable enol intermediate The enol arises by Markovnikov hydration of the alkyne Enol formation is followed by rapid isomerization of the enol to a ketone... 

Hydration and Dehydration. Maleic anhydride is hydrolyzed to maleic acid with water at room temperature (68). Fumaric acid is obtained if the hydrolysis is performed at higher temperatures. Catalysts enhance formation of fumaric acid from maleic anhydride hydrolysis through maleic acid isomerization. 

Uses ndReactions. a-Pinene (8) is useful for synthesizing a wide variety of terpenoids. Hydration to pine oil, acid-catalyzed isomerization to camphene, thermal isomerization to ocimene and aHoocimene, and polymerization to terpene resins are some of its direct uses. Manufacture of linalool, nerol, and geraniol has become an economically important use of a-pinene. 

Positionalisomeri tion occurs most often duting partial hydrogenation of unsaturated fatty acids it also occurs ia strongly basic or acidic solution and by catalysis with metal hydrides or organometaUic carbonyl complexes. Concentrated sulfuric or 70% perchloric acid treatment of oleic acid at 85°C produces y-stearolactone from a series of double-bond isomerizations, hydration, and dehydration steps (57). 

Alkynes can be hydrated in concentrated aqueous acid solutions. The initial product IS an enol, which isomerizes to the more stable ketone. 

Hydrate isomerism of TiCl3.6H20, yielding [TiCl2(H20)4]" CU as one of the isomers, has already been referred to (p. 965) and analogous complexes are formed by a variety of alcohols. Neutral complexes, [T1L3X3] have been characterized for a variety of ligands such... 

Nuclear magnetic resonance spectra of all four parent compounds have been measured and analyzed.The powerful potentialities of NMR as a tool in the study of covalent hydration, tautomerism, or protonation have, however, as yet received no consideration for the pyridopyrimidines. NMR spectra have been used to distinguish between pyrido[3,2-d]pyrimidines. and isomeric N-bridgehead compounds such as pyrimido[l,2- ]pyrimidines and in several other structural assignments (cf. 74 and 75). 

The parent compounds undergo facile hydrolysis to aminoaldehydes subsequent to the covalent hydration and reversible ring-opening as described above for pyrido[4,3-d]pjrrimidines (Section IV, B). 2-(3-Pyridyl)pyTido[2,3-d]pyrimidine undergoes hydrolysis to yield 2-aminonicotinaldehyde and nicotinamide when treated with N—HCl under reflux for 3 hours. This mechanism also probably involves a covalent hydrate. 2-Methylpyrido[4,3-d]pyrimidin-4(3H)-one, although much more stable than the parent compound, is readily hydrolyzed with dilute acid, whereas the isomeric compounds from the other three systems are stable under such conditions. 

The above method is unsatisfactory when hydration takes place at two alternative sites in the molecule, although one hydrate is usually present in only a very small proportion, at equilibrium. Which oxo compound is preferentially formed in such a case depends on the rates of oxidation at the different sites and on the rate of isomerization of the water molecule from one position to the other, hence this method does not indicate which is the thermodynamically more stable hydrate. 

At the same time, the hydration of 3(5)-phenyl-5(3)-phenylethynylpyrazole 45 in sulfuric acid in the presence of mercury acetate leads to the formation of two isomeric ketones 46 (yield 44%) and 47 (yield 3%) (68LA117) (Scheme 88). 

In aqueous solutions, the prevailing process is the primary attack of the unsubstituted nitrogen atom of alkylhydrazines at the terminal carbon atom of diacetylene with predominant formation of l-alkyl-5-methylpyrazoles (18) (73DIS). The content of isomeric l-alkyl-3-methylpyrazoles is less than 10% (GLC). In the authors opinion, this different direction of the attack at diacetylene in aqueous media is related to the hydration of alkylhydrazines and the formation of ammonium base RN" H2(0H) NH2, in which the primary amino group becomes the major nucleophilic center. 

The reaction of disubstituted diacetylenes with hydrazine hydrate was reported by Darbinyan et al. (70AKZ640). In the first stage the addition of hydrazine to the terminal carbon atom of the diacetylene system is analogous to that of primary amines to diacetylene (69ZC108 69ZC110). With monosubstituted diacetylenes (R = H), hydrazine adds to the terminal triple bond. This leads to the formation of vinylacetylenic hydrazine 22 which cyclizes to dihydropyrazole 23 subjected to further isomerization to the pyrazole 25. It is possible that hydrazine 22 undergoes hydration to the ketone 24 which can easily be cyclized to the pyrazole 25... 

There exists in East Indian sandalwood oil an alcohol, of the formula CjHjgO, which has been named santelol, or santenone alcohol. It is closely allied to, and much resembles, the alcohol obtained by the hydration of the hydrocarbon, santene q.v.), and is probably stereo-isomeric with it. There is some difference of opinion as to the proper nomenclature of the two alcohols. According to Charabot, the naturally occurring alcohol, also obtainable by the reduction of santenone, is analogous to borneol, and should therefore be termed, if that analogy is... 

This differs from the isomeric stable compound in being quantitatively decomposed by the action of sodium hydrate into citral and neutral sodium sulphite. 

In recent years, the rate of information available on the use of ion-exchange resins as reaction catalysts has increased, and the practical application of ion-exchanger catalysis in the field of chemistry has been widely developed. Ion-exchangers are already used in more than twenty types of different chemical reactions. Some of the significant examples of the applications of ion-exchange catalysis are in hydration [1,2], dehydration [3,4], esterification [5,6], alkylation [7], condensation [8-11], and polymerization, and isomerization reactions [12-14]. Cationic resins in form, also used as catalysts in the hydrolysis reactions, and the literature on hydrolysis itself is quite extensive [15-28], Several types of ion exchange catalysts have been used in the hydrolysis of different compounds. Some of these are given in Table 1. 

Clearly compound 26 (R = Ac) had undergone a reaction analogous to the glycal rearrangement. It has been demonstrated that the rearrangement of this compound also occurs at room temperature in acetic anyhydride in the presence of zinc chloride (34). Under these conditions, however, a further slower isomerization takes place and a third product, assigned the acetylated enone-hydrate structure 29, was isolated. As noted later this structure has been shown to be incorrect. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

Chromium, tetraaquadichloro-chloride dihydrate hydrate isomerism, 1, 183 Chromium, tetrabromo-solvated, 3, 758 synthesis, 3, 763 Chromium, tetrachloro-antiferromagnetic, 3, 761 ferromagnetic magnetic properties, 3,7559 optical properties, 3,759 structure, 3,759 solvated, 3. 758 synthesis. 3, 759 Chromium, tetrachlorooxy-tetraphenylarsenate stereochemistry, 1,44 Chromium, tetrahalo-, 3,889 Chromium, tetrakis(dioxygen)-stereochemistry, 1,94 Chromium, triamminediperoxy-structure. 1, 78 Chromium, tricyanodiperoxy-structure, 1, 78 Chromium, trifluoro-electronic spectra, 3, 757 magnetic properties, 3, 757 structures, 3, 757 synthesis, 3, 756 Chromium, trihalo-clcctronic spectra, 3, 764 magnetic properties, 3, 764 structure, 3, 764 synthesis, 3, 764 Chromium, tris(acetylacetone)-structure. 1, 65 Chromium, tris(bipyridyl)-... 

Cobalt, diamminedichloro(l, 2-ethanediamine)-hydrate thiocyanate isomerization, 1,469 reactions, 1,27... 

Cobalt, dichlorobis(AvY -dimethyl-1,2-ethanediamine)-chloride hydrate isomerization, 1, 468 Cobalt, dich orobis(l,2-ethanediamine)-base hydrolysis, 1, 304 chloride anation, 1, 469 halogen exchange, 1, 468 chloride hydrate isomerization, 1, 468 isomers, 1,191 nitrate... 

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