Chlorinated dehydrochlorination

Chlorination and Chlorination—Dehydrochlorination of Paraffins. Linear internal olefins were produced by Shell at Geismar from 1968 to 1988, using the dehydrochlorination of chlorinated linear paraffins, a process that also yields hydrogen chloride as a by-product. To avoid the production of dichloroparaffins, which are converted to diolefins by dehydrochlorination, chlorination of paraffins is typically limited to 10% conversion. 

The chlorination-dehydrochlorination method for producing n-y-olefins from the corresponding rc-alkanes is no longer of industrial importance [30]. 

Denis and coworkers [37] could trap transient simple phosphaalkene 33, generated by HC1 elimination from chlorophosphine 32 at low temperatures [38], by ethyl diazoacetate at -50°C. Aromatization of the initially formed isomeric E-/Z-cycloadducts 35 to [l,2,4]diazaphospholes 36 could be achieved via P-chlorination/ dehydrochlorination sequence at -30°C using /V-chIorosuccinimidc (Scheme 10). 

Scheme 15 N-Chlorination/Dehydrochlorination to Yield a,[3-Didehydro-a-amino Acid Derivatives1122-1241 R2 1. tBuOCI R2 R2...

As discussed in Section 11.1.1.2.3 most of the aliphatic DHAs such as AAla, AVal, ALeu, Alle, AAsp, AGlu, and AOrn have been prepared either by (3-elimination, N-chlorination/ dehydrochlorination, or from Af-carboxy a, 3-didehydroamino acid anhydrides which, in turn, are prepared by condensation of an a-oxo acid with benzyl carbamate. 

AVal residues can be synthesized by the condensation method or by the N-chlorination/ dehydrochlorination method. 77,149 In the condensation method, either benzylcarbamate or a benzyloxycarbonylamino acid amide is condensed with 3-methyl-2-oxobutanoic acid in benzene using 4-toluenesulfonic acid as a catalyst to obtain Z-AVal or Z-Xaa-AVal dipeptides. 150 In this case it is not possible to elongate the chain from the N-terminus because the... 

Z group can only be deprotected under strong acidic conditions or by catalytic hydrogenation. Indeed, neither of these methods is suitable for DHA-containing peptides. The other method for the synthesis of AVal peptides is the N-chlorination/dehydrochlorination, which is more useful and has been exploited in our laboratory to prepare model peptides.1381... 

The C-terminal tripeptide tail of oxytocin H-L-Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor, MIF or melanostatin) is implicated as having a direct effect on the central nervous system. The ALeu analogue of melanostatin, [ALeu2-MIF] was prepared in view of the earlier work on the active conformation of melanostatin in which a (3-turn was implicated.11771 ALeu was prepared by the N-chlorination/dehydrochlorination reaction and then coupled with Boc-Pro-OH. 

Dihydroisoquinolines. The N-chlorination-dehydrochlorination sequence with K02 (8, 417) can be used to convert 1,2,3,4-tetrahydroisoquinoline (1) to 3,4-dihydroisoquinoline (2) and 1-substituted tetrahydroisoquinolines (3). ... 

The paraffins made can be separated and after suitable treatment, recycled to a dehydrogenation unit such as a chlorination - dehydrochlorination unit to reform the olefin. This improves the overall yield. 

The synthesis of 3-chloroisothiazole from 3-mercaptopropionitrile and chlorine58 (Scheme 19) may be envisaged as occurring by a similar mechanism with an additional chlorination-dehydrochlorination stage either before or after eyclization. 

Another route for the synthesis of 3-oxazolines is via a chlorination/dehydrochlorination sequence of 1,3-oxazoli-dines, for example, 268 <2000TL9787>. This net oxidation reaction results in mixtures of 2- and 3-oxazolines (269 and 270, respectively) with the product ratios dependent on the nature of the base used (Equation 14). 

Normal Paraffin-Based Olefins, Detergent range -paraffins are currently isolated from refinery streams by molecular sieve processes (see ADSORPTION, LIQUID separation) and converted to olefins by two methods. In the process developed by Universal Oil Products and practiced by Enichem and Mitsubishi Petrochemical, a -paraffin of the desired chain length is dehydrogenated using the Pacol process in a catalytic fixed-bed reactor in the presence of excess hydrogen at low pressure and moderately high temperature. The product after adsorptive separation is a linear, random, primarily internal olefin. Shell formedy produced olefins by chlorination—dehydrochlorination. Typically, C —C14 -paraffins are chlorinated in a fluidized bed at 300°C with low conversion (10—15%) to limit dichloroalkane and trichloroalkane formation. Unreacted paraffin is recycled after distillation and the predominant monochloroalkane is dehydrochlorinated at 300°C over a catalyst such as nickel acetate [373-02-4]. The product is a linear, random, primarily internal olefin. 

Vinylchlorosilanes are prepared most conveniently from ethylchlorosilanes by a modification of the chlorination-dehydrochlorination reactions in which the dehydrohalo-genation is effected by a high-boiling tertiary amine. Although the experimental procedure herein described is based on the preparation of vinyltrichlorosilane, the method can be adapted to the synthesis of many other vinyl silicon compounds. 

Without this type of process, ethylene-based VCM would be responsible for a glut of HCl. With the right combination of direct chlorination, dehydrochlorination, and oxychlorination (Eqs. 2, 3, and 8), die production and consumption of HCl can be balanced (Fig. 15.6). The theoretical requirement of chlorine is cut in half from that called for by Eqs. (2) and (3). While Fig. 15.6 shows the production of VCM with the aid of oxychlorination, it is also possible to stop with the synthesis of EDC. The HCl in this case may be the byproduct of another process. This approach has the advantage of a less volatile and less toxic product more suitable than either chlorine or VCM for export. 

Alkylthioketones are obtained by aldol-type condensations of simple ketones with formaldehyde and a thiol. a-Alkylthio-a -unsaturated carboxylate derivatives may be prepared by Stobbe-type condensations of 5-ethylthioglycollate with aldehydes, or by chlorination-dehydrochlorination of the saturated a-alkyl-thiocarbonyl compounds. ... 

Chloroethene (vinyl chloride) is made from ethene by a chlorination-dehydrochlorination sequence in which addition of CI2 produces 1,2-dichloroethane. This compound is converted into the desired product by elimination of HCl. 

At present, it is produced by the chlorination-dehydrochlorination of butadiene according to the following reaction pathway ... 

A route to a-enaminocarboxylic acid esters based on N-chlorination/ dehydrochlorination of amino acid esters has been described by H. Poisel and U. Schmidt 312, 313). N-Chlorination of BOC-amino acid esters followed by dehydrochlorination with methoxide affords a-methoxy-a-BOC-amino acid esters (41), which, on treatment with HCl, undergo elimination of methanol and cleavage of the protective group in a single step. The free enamino esters (42) are liberated from their hydrochlorides by treatment with ammonia or triethylamine. NMR spectroscopic studies showed that (42a) and (42c) exist exclusively in the enamino tautomeric form, while (42b) contains about 40% imino tautomer. 

N-Chlorination/dehydrochlorination of amino acid esters 310) is the simplest route to a-iminocarboxylic acid esters. With the exception of the leucine derivative, which was obtained as a tautomeric mixture, no enamine could be detected in the products by NMR spectroscopy. Phenylalanine ester yielded the enaminoacid ester exclusively. 

Fig. 3. Routes to linear alkylbenzene chlorination, dehydrochlorination and alkylation with Friedel-Crafts catalysts and subsequent sulfonation to alkylbenzenesulfonate...

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