Chlorides secondary

Secondary or tertiary alkyl halides are much less reactive. For example an alkyl dichloride with a primary and a secondary chloride substituent reacts selectively by exchange of the primary chloride. The reactivity with respect to the Finkelstein reaction is thus opposite to the reactivity for the hydrolysis of alkyl chlorides. For the Finkelstein reaction on secondary and tertiary substrates Lewis acids may be used," e.g. ZnCla, FeCls or MesAl. 

Secondary Chlorides With a low-boiling chloride such as 2-chlorobutane, a stirred slurry of 30 g (0.61 mole) of sodium cyanide in 150 ml of dimethyl sulfoxide is heated to 90° with a heating mantle, and 0.5 mole of the chloride is slowly added over a period of 30 minutes. The temperature of the refluxing reaction mixture slowly increases as nitrile is formed. Refluxing continues as the temperature slowly rises to 150° after 3 hours reaction time. The flask is then cooled and the reaction mixture is worked up in the same way as for the primary nitriles. With 2-chlorooctane, the sodium cyanide-dimethyl sulfoxide slurry is heated to 130° and 0.5 mole of the chloride added. The reaction mixture is maintained at 135-145° for 1 hour, then cooled, and the product is isolated as above. Examples are given in Table 16.1. 

The two remaining isomers are a secondary chloride and a tertiary chloride ... 

The iodo and bromo derivatives of monosaccharides can be reduced by a variety of reducing agents to afford the corresponding deoxy sugar. Many such examples have been presented. The more stable chloro derivatives can be reduced with Raney nickel (Scheme 1). Selective reduction of a secondary chloride with respect to a primary chloride may be achieved if the reduction is performed in the presence of triethylamine.11,12 Selective reduction of a secondary chloride has been also achieved by using organotin hydrides.13 The radical initiator... 

Relative to tertiary alkyl halides, secondary derivatives react considerably slower. At room temperature and long reaction periods ( 24h) cyclohexyl chloride is almost quantitatively methylated with dimethyltitanium dichloride (prepared in situ from dimethylzinc and catalytic amounts of TiQ4)137>, but other cyclic or acyclic halides tend to undergo competing rearrangements prior to C—C bond formation 77). The same applies to 1,2-dihalides such as 1,2-dibromocyclohexane which affords 1,1-dimethylcyclohexane instead of the 1,2-dimethyl derivative137. In complete contrast, activated secondary chlorides behave much like tertiary derivatives, i.e., methylation is fast and position specific at low temperatures. Examples are shown in Equation 86137>. It should be noted that in such cases cuprate chemistry affords less than 40 % of methylation products138). 

A reagent wiiich may operate by hydrogen atom abstraction fr n the alkane by the intormediaie alkyl-ammonium radical cation is iron(II)/R2NCl/CF3C02H, which affords secondary chlorides in good yield from R-alkanes without overoxidation. 

More isomeric octyl chlorides than hexyl chlorides were formed by a telomerization reaction involving a second molecule of ethylene. Nuclear magnetic resonance (nmr) suggested that the product was a mixture of about equal weight of primary and secondary chlorides. Since many octyl chloride isomers exist, no conclusion was reached as to the probable structures. 

Several conjugated diolefins have been made by heating bromo olefins with solid potassium hydroxide or excess quinoline. In the latter case, the bromo olefins were made available by allylic bromination of olefins with N-bromosuccinimide. /S-phenylbutadiene is obtained in 46% yield by the action of pyridine on the corresponding secondary chloride. Chlorination of n-butyl chloride gives an isomeric mixture of dichlorides from which low yields (18-30%) of butadiene are obtained by passing the vapors over soda lime at about 700°. ... 

Secondary chlorides of propane and butane can be made without side reactions from isopropyl alcohol and s-butyl alcohol by treatment with HCl and ZnCl, in the cold however, treatment of the next higher homolpg 3-pentanol under the same conditions gives a mixture of chloropentanes. The 2- and 3-chloropentanes are best obtained by the SOClj-pyridine procedure. The corresponding bromo derivatives have been obtained using hydrogen bromide at a low temperature however, care must be taken to avoid isomerization. 

Support for the c/j-nature of the elimination reaction has come from the work of Barton et on the pyrolysis of menthyl chloride, and the results of this study have recently been confirmed by Bamkole > who also examined the pyrolysis of neomenthyl chloride. The product ratio of menthene-3 to methene-2 is 3 1 in the case of menthyl chloride and 1 6 in the case of neomenthyl chloride, thus demonstrating a preference for m-elimination in each case. These two decompositions do, however, have some unusual characteristics the Arrhenius parameters are considerably lower than those reported for other secondary chlorides, and the rate of elimination of hydrogen chloride from each compound is appreciably faster than from cyclohexyl chloride . (The relative rate of pyrolysis of menthyl chloride and cyclohexyl chloride at 300 °C is about fifty.)... 

In the mass spectrometer, processes (1) and (2) are comparable for ethyl chloride, but ion formation by process (2) occurs more readily for higher n-alkyl chlorides. Process (1) is of increasing importance for secondary chlorides and most important for tertiary chlorides. It is also of major significance in the case of methyl and aromatic chlorides. 

Finally, when the selective reduction of secondary centers is desired over primary centers, free radical chemistry provides the answer. Unlike ionic mechanisms, the formation of free radicals occurs more readily at tertiary centers, with secondary radicals being more stable than primary radicals. As shown in Scheme 6.72, tributyltin hydride sequentially removed the secondary chloride with complete reduction of both chlorides over extended reaction times [111]. 

The reaction of thionyl chloride SOCI2 (43) with the secondary allylic alcohol 22 first gives chlorosulfite 45, which is not stable but eliminates SO2 with formation of the rearranged primary allyl chloride 47 (path a) or of a secondary chloride 49 (path b). Such reactions are termed "SNi"-reactions, for intemal" substitution reactions. Since the cyclic six-membered transition state 46 for path a is lower in energy, 47 is selectively formed at -78 °C. From the transition state it can be seen why only the -configured product is obtained. When this reaction is performed at a higher temperature, side product 49 is formed in isolable amounts. 

Butyl chlorides. As stated in the preceding paragraphs, tertiary alcohols react rapidly with halogen acids. If excess of hydrochloric acid is used, the tertiary halide is formed at room temperatures. n-Butyl and sec-butyl alcohols require heating with a mixture of concentrated hydrochloric acid and fused zinc chloride in order to yield appreciable amounts of the normal and secondary chlorides. It should be noted that the ease of formation of the halide corresponds to the ease of hydrolysis. This should be expected if we consider the following equation ... 

An exception to these general principles which has been reported is the reaction of a- or 7-ethylallyl alcohol with thionyl chloride. The primary isomer gives principally the secondary chloride, and from the secondary isomer the primary chloride predominates.4 It has been pointed out, however,5 that these results may be explained by an Sni type reaction of the intermediate chlorosulfinic ester in which a six-membered ring is involved. Thus for the transformation of a-ethylallyl alcohol (VIII) to 7-ethallyl chloride (IX), we have ... 

With regard to interaction with isobutene monomer the structure of the carbon skeleton of the alkyl halide is also vitally important. Thus with (C2H5)2A1C1 initiator, tertiary chlorides are many orders of magnitude more active than simple primary or secondary chlorides, presumably because of the relative ease of formation of the corresponding cations. However, generation of too stable a carbocation, e.g. PhaC" from PhaCCl, results in no polymerization at all. 

Systematic data on the relation between chemical structure or reactivity of chlorine compounds and lubricant additive performance are sparse. Table 11-11 gives some four-ball test data obtained by Mould, Silver and Syrett [35], with the additives listed in order of increasing effectiveness in terms of the wear/load index. The results show numerous departures from expectations based on chemical structure. For example, there is practically as much difference between the wear/load indices for the two primary chlorides, n-hexadecyl (16.2 kg) and n-hexyl (30.4 kg), as for n-hexyl chloride and t-butyl chloride (46.1 kg). A large difference would be expected on the basis of chemical reactivity between the additive effectiveness of primary and tertiary alkyl chlorides, but only a small difference for the two primary aliphatic chlorides. The overall trends are what would be expected in general, primary and aromatic chlorides are less efficacious than secondary chlorides, which in turn... 

The energy difference between the anti and syn transition structures has been examined computationally using fluoride as the base and alkyl chlorides as the reactants. Simple primary and secondary chlorides show no barriers for anti elimination at the MP4SDQ/6-31+G level. The syn TSs show positive barriers and the total difference between the syn and anti TSs is on the order of 13 kcal/mol. ... 

These authors31 also reported that the desulphonylation reaction of the mixture of 19 and 32 was endothermic by 3.6kcalmol-1 and resulted in a mixture of primary and secondary chlorododecanes (33 and 34) they could also form by direct chlorination of the hydrocarbon. The heat of formation of 1-chlorododecane (33) is well established as —93.8 + 0.6 kcal mol l. Let us assume that the difference between heats of formation of isomeric primary and secondary chlorides is a constant, and so <5A/Jf(lq, 33, 34) = <5AHf(lq, n-PrCl, i-PrCl) = 2.7 + 0.5 kcal mol-1. [Interestingly, there are no reliable data for any isomeric pair of alkyl chlorides save these propyl chlorides—for 1- and 2-chlorobutane 35a and 35b, <5AHf(lq, 35a, 35b) = 1.1 + 2.0 kcal mol - The heats of formation of any of the various liquid secondary chlorododecanes lumped together here as 34 are all ca... 

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