Rearrangement molecular

Spiropyrans, and spirooxazines, better known for their photochromic behaviour (see sections 1.22 and 1.23), also exhibit thermochromism. The ring opening to produce the highly coloured merocyanine form is induced by heating either the solid or 

This reaction constitutes an acid-catalyzed Hofmann rearrangement [34, 35]. The trifluoroacetic acid formed in the reaction hydrolyzes the intermediate isocyanate and protonates the amine as it forms preventing further reaction. 

1 Rearrangement to Electron-Deficient Oxygen The Baeyer-Villiger oxidation, like the Hock rearrangement, is an example of a molecular rearrangement to oxygen. Examples are shown in Equations 6.9 and 6.10. The 

The mechanism shown uses m-chloroperoxybenzoic acid (mCPBA) as the oxidant. The enzymatically catalyzed reaction uses molecular oxygen. The reaction is considered a kinetic resolution, discussed further in Section 3.4. The enzyme reacts faster with the S enantiomer, allowing formation of the S lactone and separation of the unreacted R ketone, which can be converted to the R lactone using traditional Baeyer-Villiger conditions [36]. 

3 Rearrangement of Electron-Deficient Carbon Carbocation rearrangements are well known. One named example is the pinacol rearrangement, the mechanism and stereochemistry of which have been well studied. 

The NIST Kinetics Database lists rate parameters for more than 38,000 reactions, http //kinetics.nist.gov/kinetics/welcome.jsp (J. A. Manion, R. E. Huie, R. D. Levin, D. R. Burgess Jr., V. L. Orkin, W. Tsang, W. S. McGivern, J. W. Hudgens, V. D. Knyazev, D. B. Atkinson, E. Chai, A. M. Tereza, C.-Y. Lin, T. C. Allison, W. G. Mallard, 

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Property Improvement Processes Using Molecular Rearrangement ... 

Urea (the diamide of carbonic acid) can be prepared by the historic method of Wohler. When an aqueous solution of ammonium cyanate is allowed to stand, the cyanate undergoes molecular rearrangement to urea, and an equilibrium mixture containing about 93% of urea is thus formed. Urea is... 

Mono-substituted and unsymmetrical di-substituted ureas may be prepared by a modification of Wohler s urea synthesis, salts of primary or secondary amines being used instead of the ammonium salt for interaction with potassium cyanate. Thus when an aqueous solution containing both aniline hydrochloride and potassium cyanate is heated, aniline cyanate is first formed, and then C,HjNH,HCl -h KCNO = C,H6NHj,HCNO -h KCl C,HsNH HCNO = C.H NHCONH, by the usual molecular rearrangement is converted into monophenyburea. 

These substances, having the formula CjHjNHCONH, and OC(NHCjH6)j respectively, are both formed when an aqueous solution of urea and aniline hydrochloride is heated. Their subsequent separation is based on the fact that diphenylurca is insoluble in boiling water, whereas monophenylurea is readily soluble. The formation of these compounds can be explained as follows. When urea is dissolved in water, a small proportion of it undergoes molecular rearrangement back to ammonium cyanate, an equilibrium thus being formed. 

When benzii is heated with potassium hydroxide solution, it undergoes a molecular rearrangement with the formation of the potassium salt of benzilic acid, or diphenyl lycollic acid ... 

Salts of primary aromatic amines react with solutions of alkali cyanates to yield first the amine cyanate, which then undergoes molecular rearrangement to the arylurea, for example ... 

There are a great many aspects to the Friedel-Crafts method that Strike does not have the space to go into. Friedel-Crafts works better if chloro or bromobenzene and their X counterparts are used in place of plain old benzene. Also, there is a significant amount of unwanted byproducts and molecular rearrangements that accompany this sort of reaction. Strike strongly suggests that people read more about this method before they attempt any such reaction. 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Antithetic conversion of a TGT by molecular rearrangement into a symmetrical precursor with the possibility for disconnection into two identical molecules. This case can be illustrated by the application of the Wittig rearrangement transform which converts 139 to 140 or the pinacol rearrangement transform which changes spiro ketone 141 into diol 142. 

Since the foregoing summary was prepared a preliminary account of an ingenious explanation of these results, involving a molecular rearrangement of a new type, has been published by Robinson which cannot be adequately dealt with here and for which the reader must be referred to the original. 

The formation of enamines from carbonyl compounds and secondary amines usually entails as only questionable structural feature, the possible isomeric position of double bonds in the product. Molecular rearrangements have not presented synthetic limitations. A notable exception is the generation of o-aminophenols on distillation of enamines derived from 2-acylfurans 620,621). 

In this review an attempt is made to discuss all the important interactions of highly reactive divalent carbon derivatives (carbenes, methylenes) and heterocyclic compounds and the accompanying molecular rearrangements. The most widely studied reactions have been those of dihalocarbenes, particularly dichlorocarbene, and the a-ketocarbenes obtained by photolytic or copper-catalyzed decomposition of diazo compounds such as diazoacetic ester or diazoacetone. The reactions of diazomethane with heterocyclic compounds have already been reviewed in this series. ... 

Reaction of 8-aminoquinoline 567 with 3,4-dichlorodithiazolium chloride gave the quinolyl iminodithiazole 568 whose thermal rearrangement gave 569 via a molecular rearrangement process (96MI2775) (Scheme 95). 

It is possible, however, that camphene hydrochloride is not a uniform body, but that some of the terpene suffers some rearrangement in the molecule by the action of hydrochloric acid, and that the hydrochloride consists of a mixture of a-camphene hydrochloride and /8-camphene hydrochloride there is, however, no evidence to suggest that camphene itwlf is a mixture of two terpenes, so that the two camphenes are not known to exist. Aschan obtained an alcohol, camphene hydrate, by acting on camphene hydrochloride with milk of lime, a reagent which does not produce molecular rearrangement in the terpene nucleus. 

Considerable difference of opinion exists as to the relationships of sabinene to terpinene, and the conversion of sabinene into terpinene hydrochloride is to be explained by a molecular rearrangement, and cannot be said to be evidence of relationship. ... 

When the dihydrochloride above mentioned is produced, it is probable that molecular rearrangement takes place and that the compound is really the dihydrochloride of a bicyclic mo-zingiberene. According to Semmler and Becker when zingiberene is treated with acetic and sulphuric acids, it is converted into MO-zingiberene. This sesquiterpene has the following characters —... 

It forms a dihydrochloride melting at 79° to 80°. The sesquiterpene regenerated from the dihydrochloride has slightly different characters, so that a molecular rearrangement is probable and the regenerated eudesmene may contain another sesquiterpene. Its characters are as follows —... 

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