2-chloro reactivity

The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

Dinitrophenylhydrazine is a very important reagent for the identification of aldehydes and ketones (pp. 342, 346). It is readily prepared from chloro-2,4-dinitrobenzene (I). In the latter compound the chlorine is very reactive in... 

The success of the last reaction depends upon the inertness of the ester carbonyl groups towards the organocadmium compound with its aid and the use of various ester acid chlorides, a carbon chain can be built up to any reasonable length whilst retaining a reactive functional group (the ester group) at one end of the chain. Experimental details are given for l-chloro-2-hexanone and propiophenone. The complete reaction (formation of ketones or keto-esters) can be carried out in one flask without isolation of intermediates, so that the preparation is really equivalent to one step. 

Table 9.7 contains recent data on the nitration of polychlorobenzenes in sulphuric acid. The data continue the development seen with the diehlorobenzenes. The introduetion of more substituents into these deactivated systems has a smaller effect than predicted. Whereas the -position in ehlorobenzene is four times less reactive than a position in benzene, the remaining position in pentachlorobenzene is about four times more reactive than a position in 1,3,4,5-tetraehlorobenzene. The chloro substituent thus activates nitration, a circumstance recalling the faet that o-chloronitrobenzene is more reactive than nitrobenzene. As can be seen from table 9.7, the additivity prineiple does not work very well with these compounds, underestimating the rate of reaction of pentachlorobenzene by a factor of nearly 250, though the failure is not so marked in the other cases, especially viewed in the circumstance of the wide range of reactivities covered. 

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

Since the exocyclic sulfur is more reactive in the ambident anion than in A-4-thiazoIine-2-thione. greater nucleophilic reactivity is to be expected. Thus a large variety of thioethers were prepared in good yields starting from alkylhalides (e.g.. Scheme 38 (54, 91, 111, 166-179). lactones (54, 160), aryl halides (54, 152. 180, 181), acyl chlorides (54. 149, 182-184). halothiazoles (54, 185-190), a-haloesters (149. 152. 177. 191-194), cyanuric chloride (151). fV.N-dimethylthiocarbamoyl chloride (151, 152. 195. 196), /3-chloroethyl ester of acrylic acid (197), (3-dimethylaminoethyl chloride (152). l,4-dichloro-2-butyne (152), 1,4-dichloro-2-butene (152), and 2-chloro-propionitrile (152). A general... 

The use of a-bromoaldehydes, more reactive than the a-chloro derivatives, gives better results (492,512). They have permitted the yields of the cyclization to be increased from 8 to 60% in the latter case. With the higher aldehydes the yields decrease. Thus for 5-f-butylthiazole it is not higher than 7 to 20% (492, 512). On the other hand, cr-bromoaldehydes are particularly difficult to obtain. 

Examples of commercial reactive duoroaromatics are not restricted to duoronitroben2enes. The duorine-free diuretic, furosemide [54-31-9], is prepared in 85% yield from 2-duoro-4-chloro-5-sulfamoylben2oic acid and furfurjlamine at 95°C for 2 h (155). 

Chloro-2,4,6-trifluoropyrimidine [697-83-6] has gained commercial importance for the production of fiber-reactive dyes (465,466). It can be manufactured by partial fluoriaation of 2,3,5,6-tetrachloropyrimidine [1780-40-1] with anhydrous hydrogen fluoride (autoclave or vapor phase) (467) or sodium fluoride (autoclave, 300°C) (468). 5-Chloro-2,4,6-trifluoropyrimidine is condensed with amine chromophores to provide the... 

Fluorochloro, fluorobromo, and fluoroiodoalkanes react selectively with aromatics under boron trifluoride catalysis to provide chloro-, bromo- and iodoalkylated products (48). The higher reactivity of the C—F bond over C—Cl, C—Br, and C—I bonds under Lewis acid catalysis results in the observed products. 

The organic iodine compounds have lower heats of formation and greater reactivities than their chloro and bromo analogues. As ia the case of the inorganic iodides, their iadexes of refraction and specific gravities are higher than the corresponding chloro and bromo derivatives (121). 

Bromination of isoprene using Br2 at —5 ° C in chloroform yields only /n j -l,4-dibromo-2-methyl-2-butene (59). Dry hydrogen chloride reacts with one-third excess of isoprene at —15 ° C to form the 1,2-addition product, 2-chloro-2-methyl-3-butene (60). When an equimolar amount of HCl is used, the principal product is the 1,4-addition product, l-chloro-3-methyl-2-butene (61). The mechanism of addition is essentially all 1,2 with a subsequent isomerization step which is catalyzed by HCl and is responsible for the formation of the 1,4-product (60). The 3,4-product, 3-bromo-2-methyl-1-butene, is obtained by the reaction of isoprene with 50% HBr in the presence of cuprous bromide (59). Isoprene reacts with the reactive halogen of 3-chlorocyclopentene (62). 

A/-Chloro fatty acid amides have been synthesized from the direct halogenation of the amide in boiling water (28). They are useful as reactive intermediates for further synthesis. Fluorination has also been reported by treating the fatty amide with fluorine-containing acid reagents at 200 °C to reach a fluorinated amide with less reactivity toward fluorocarbon polymers (29). 

Halothane. Halothane or Fluothane, 2-bromo-2-chloro-l,l,l-trifluoroethane [151 -67-7] is a colorless Hquid with a pleasant odor. Its lower flammability limit, 4.8% in 70% N2O/30% O2, renders it essentially nonflammable. It has a vapor pressure of 32.5 kPa (244 mm Hg) at 20 °C and is stable to soda lime. However, it is photochemicaHy reactive. 

The ratio between the isomers obtained in coupling with 1,3- and 1,5-naphtholsulfonic acids depends on the reactivity of the diazo component. Energetic ones, such as the 2,4-dinitrobenzenediazonium compound, essentially couple only with l-naphthol-3-sulfonic acid [3771-14-0] in the para position, but 4-chloro-benzenediazonium salt (a weaker diazo) attacks the ortho position. Both isomers result when mononitrobenzenediazonium compounds are used. The tendency to couple para is greater in l-naphthol-5-sulfonic acid [117-59-9] C QHgO S (21). For the combination of... 

Generally, the reactions of halopyrazines and haloquinoxalines with nucleophiles are believed to proceed by way of addition/elimination sequences, although there are clear-cut examples where this is not the case (see Section 2.14.2.2) and, consistent with a mechanism which involves bond forming, rather than bond breaking, reactions in the rate-determining step, fluoro derivatives are considerably more reactive ca. xlO ) than the corresponding chloro derivatives. 

The 5-chloro in 5-deazaflavins is reactive (7SJHC181), but not the 8-chloro, in contrast to the flavin case (79LA1802), and 4-chloropyrimido[4,5-Z>]quinolinium salts are readily hydrolyzed (76JCS(Pl)l3l). 

In the 7-phenyl-l,4,5-trichloro compound (335), however, the 5-chloro was the most reactive with amines, followed by the 1-chloro and finally the 4-chloro (75CPB2306). 

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