Type C reactions

In the indazole series an example of a type (c) reaction (Figure 25) has been described utilizing a 1,3-dipole instead of a diene (Scheme 32) (76H(4)1655). The cycloadduct (351) is transformed into the triazole (352) on reaction with hydrochloric acid. 

Figure 223. Types of chemical heat pump (a) reaction phase change batch type, (b) reaction reaction batch type, (c) reaction separation work continuous type...

An interesting example for the type C reaction is the simultaneous reaction of I with alcohol/amine mixtures. In the case of Ic the reaction can be controlled in such a way, that practically exclusively the esteramide of the dithiophosphoric acid is formed (8) ... 

By comparison of the mass spectra of alkanes with those of compounds containing a heteroatom, it is apparent that the heteroatom has a marked effect on the spectrum, as in type B cleavages (29). The heteroatom helps to stabilize the fragment ions, as further illustrated by the type C reaction (30). 

Chiara et al. also reported the type [C] reaction, the cyciization between carbonyl compounds and oximes [220,221]. As illustrated in O Fig. 17, three types of substrate were s)uithesized from hexopyranoses and pentopyranoses, and the terminal O-benzylformaldoxime-ketones and the terminal O-benzylformaldoxime-a, /3-unsaturated esters were synthesized from a series of hexopyranoses, and meanwhile the terminal O-benzylformaldoxime-aldehydes were derived from a series of pentopyranoses (O Fig. 17). 

Type C reactions are considered as slow t. > 10 min). They are normally carried out in batch-wise operated vessels. Nevertheless, microstructured devices may be advantageous, if safety or product quality is an important issue. 

A small number of Type C reactions cause real scale-up problems (around 6% only as indicated in Figure 13.3). Therefore, it is not surprising to observe that the reaction mixture is generally diluted for the majority of slow reactions. It seems that from the very beginning, the process development chemist approaches the scale-up problem by diluting the reaction mixture. The use of solvent is a pragmatic approach to avoid future scale-up problems however, it renders the process inefficient with a high consumption of raw materials. 

Type C reactions are slow, where the reaction times are of the order of greater than 10 min. These reactions are well suited for batch processing, but safety and quality are issues that need to be handled. 

Strike couldn t find any decent nitroethane synths except for a couple of Chemical Abstract articles. One suggestion is to treat 1.5 moles of Na2C02 with 1 mole of sodium ethylsulfite and 0.0645 moles of K2CO3 at 125-130°C. Another route would be to use silver nitrate and ethyl iodide [8 p119]. This type of reaction has been used to nitrate other paraffins and would probably work. 

Alcohols can be synthesized by the addition of carbanions to carbonyl compounds (W.C. Still, 1976) or epoxides. Both types of reactions often produce chiral centres, and stereoselectivity is an important aspect of these reactions. 

Stereoselectivities of 99% are also obtained by Mukaiyama type aldol reactions (cf. p. 58) of the titanium enolate of Masamune s chired a-silyloxy ketone with aldehydes. An excess of titanium reagent (s 2 mol) must be used to prevent interference by the lithium salt formed, when the titanium enolate is generated via the lithium enolate (C. Siegel, 1989). The mechanism and the stereochemistry are the same as with the boron enolate. 

When the substituent on the nitrogen atom is -CH-C-R, R = H, Me, Rj = Ph. Me. two types of reactions can occur, according to the nature of the medium in which the base is allowed to react ... 

A quote from a biochemistry text IS instructive here This IS not an easy reaction in or game chemistry It is how ever a very important type of reaction in metabolic chemistry and is an integral step in the oxidation of car bohydrates fats and several ammo acids G L Zubay Biochemistry 4th ed William C Brown Publishers 1996 p 333... 

Substitution of various groups by amino or hydroxyl functions is industrially unimportant for the production of 2- and 4-aminophenol, but this type of reaction is used for the synthesis of 2- and 4-aminophenol derivatives. However, 3-aminophenol caimot be obtained easily by reduction. It is made by the reaction of 3-aminobenzenesulfonic acid [121 -47-1] with sodium hydroxide under fusion conditions (5—6 h 240—245°C). The product is purified by vacuum distillation (25). 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Nucleophilic Substitutions of Benzene Derivatives. Benzene itself does not normally react with nucleophiles such as haUde ions, cyanide, hydroxide, or alkoxides (7). However, aromatic rings containing one or more electron-withdrawing groups, usually halogen, react with nucleophiles to give substitution products. An example of this type of reaction is the industrial conversion of chlorobenzene to phenol with sodium hydroxide at 400°C (8). 

Radical decomposition is one of the most important types of reactions. In this case, a larger radical decomposes to an olefin and a smaller radical. Radicals usually decompose at the beta position of the radical center where the C—C bond is the weakest. In the case of naphthenes and aromatics this may not be the case, and C—H bond may be the weakest. Radical isomerization frequently occurs for large radicals, and explains to a large extent the observed product distribution. 

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