Tertiary chlorinated carbon

In this lecture some new routes to phosphorus-carbon compounds with P-C multiple bonds, found in connection with our investigations on reactions of tertiary phosphanes with chlorinated carbon compounds, such as tetrachloromethane, hexachloroethane, phosgene, and isocyanide dichlorides are reported. Furthermore some stereochemical problems concerning this type of compound will be discussed. 

Alkyl halides are hydrolyzed to alcohols by water or dilute bases, the order of reactivity of the halogen atoms being tertiary > secondary > primary and iodine > bromine > chlorine. By heating 1,2-dichloro-2-methyl-propane, (CHj),CClCH,Cl, with an aqueous suspension of calcium carbonate, the tertiary chlorine atom is replaced to give 1-chloro-2-methyl-2-propanol (48%). ... 

Reductions with tributyltin deuteride (BujSnD) showed that the microstructure of the butyl branches is 2,4-dichlorobutyl with a chlorine attached to the branch carbon, i.e. a tertiary chlorine. 

It was also shown that the major part of the long chain branches (LCB) also contain tertiary chlorine but the presence of hydrogen at the LCB branch carbon could not be excluded. 

Despite much investigation, the mechanism of thermal hydrogen chloride elimination is still disputed. It was originally assumed that the dehydrochlorination started at the tertiary chlorine atoms. But, according to recent evidence, PVC does not have any tertiary chlorine atoms. However, there are about 0.5-1.5 double bonds per 1 000 carbon atoms. The dehydrochlorination should start at these double bonds and proceed further by an unzipping reaction ... 

Dichloroketene as a component for this 2 + 2-cycloaddition, however, introduces a new problem for the Faworski-reaction. The a,a-dihalocyclobutanones are not suited for the rearrangement of the carbon skeleton. Instead, the tertiary chlorine atom is transferred to the other a-position under basic conditions to give a,a -dihalocyclobutanones 248 [495] (Reaction schemes 172, 173 see also page 43). Even... 

It consists in treating a solution of sodium iodide in pure acetone with the organic compound. The reaction is probably of the S 2 type involving a bimolecular attack of the iodide ion upon the carbon atom carrying the chlorine or bromine the order of reactivities of halides is primary > secondary > tertiary and Br > Cl. 

Oxidation. Disulfides are prepared commercially by two types of reactions. The first is an oxidation reaction uti1i2ing the thiol and a suitable oxidant as in equation 18 for 2,2,5,5-tetramethyl-3,4-dithiahexane. The most common oxidants are chlorine, oxygen (29), elemental sulfur, or hydrogen peroxide. Carbon tetrachloride (30) has also been used. This type of reaction is extremely exothermic. Some thiols, notably tertiary thiols and long-chain thiols, are resistant to oxidation, primarily because of steric hindrance or poor solubiUty of the oxidant in the thiol. This type of process is used in the preparation of symmetric disulfides, RSSR. The second type of reaction is the reaction of a sulfenyl haUde with a thiol (eq. 19). This process is used to prepare unsymmetric disulfides, RSSR such as 4,4-dimethyl-2,3-dithiahexane. Other methods may be found in the Hterature (28). 

Primary alkyl chlorides are fairly stable to fluorine displacement. When fluorinated, 1-chloropropane is converted to 1-chloroheptafluoropropane and 1-chloto-2-methylbutane produces 39% l-chlorononafluoro-2-methylbutane and 19% perfluoro-2-methylbutane. Secondary and tertiary alkyl chlorides can undergo 1,2-chlorine shifts to afford perfluonnated primary alkyl chlorides 2-Chloro-2-methylpropane gives l-chlorononafluoro-2-methylpropane, and three products are obtained by the fluorination of 3-chloropentane [7] (equation 1). Aerosol fluorina-tion of dichloromethane produces dichlorodifluoromethane which is isolated in 98% purity [4 (equation 2). If the molecule contains only carbon and halogens, the picture is different. Molecular beam analysis has shown that the reaction of fluorine with carbon tetrachlonde, lodotrichloromethane, or bromotrichloromethane proceeds first by abstraction of halogen to form a trichloromethyl radical [5]... 

It has been proposed that aromatic solvents, carbon disulfide, and sulfur dioxide form a complex with atomic chlorine and that this substantially modifies both its overall reactivity and the specificity of its reactions.126 For example, in reactions of Cl with aliphatic hydrocarbons, there is a dramatic increase in Ihe specificity for abstraction of tertiary or secondary over primary hydrogens in benzene as opposed to aliphatic solvents. At the same time, the overall rate constant for abstraction is reduced by up to two orders of magnitude in the aromatic solvent.1"6 The exact nature of the complex responsible for this effect, whether a ji-coinplex (24) or a chlorocyclohexadienyl radical (25), is not yet resolved.126- 22... 

Alkyl Side Chains of Aromatic Rings. The preferential position of attack on a side chain is usually the one a to the ring. Both for active radicals such as chlorine and phenyl and for more selective ones such as bromine such attack is faster than that at a primary carbon, but for the active radicals benzylic attack is slower than for tertiary positions, while for the selective ones it is faster. Two or three aryl groups on a carbon activate its hydrogens even more, as would be expected from the resonance involved. These statements can be illustrated by the following abstraction ratios ... 

Chlorine reacts with a hydrocarbon by substituting for one or more hydrogens. The easiest hydrogen to remove in this manner is from a tertiary carbon, next a secondary, and the least readily from a primary carbon. Where more than one type of carbon is present, as in isopentane, a mixture of compounds containing chlorine will be produced. 

These trends were further confirmed through reactions of the foregoing chiral carbonate and phosphate derivatives with other electrophiles (Eqs. 9.32-9.34) [39]. For example, on protonolysis or deuterolysis, the allenyltitanium intermediate derived from the tertiary carbonate of Eq. 9.32 afforded an alkyne of 90% enantiopurity. Based on the configuration of this product and the assumption of a syn elimination to form the allenyltitanium, the protonolysis was suggested to take place by a syn SE2 pathway. In contrast, chlorination of this allenyltitanium intermediate follows an anti pathway (Eq. 9.33). 

Tertiary alkyl halides are easier to reduce than secondary alkyl halides, which are easier to reduce than primary alkyl halides. Carbon-iodine bonds are easier to reduce than carbon-bromine bonds, which are easier to reduce than carbon-chlorine bonds [1-3]. 

Primary treatment (solid settling and removal) is required, secondary treatment (use of bacteria and aeration to enhance organic degradation) is becoming more routine, and tertiary treatment (filtration through activated carbon, applications of ozone, and chlorination) has been, or is being, implemented by all refineries. 

Advanced wastewater treatment techniques, for example oxidation processes, can achieve up to 100% removal for diclofenac [52,53], Reverse osmosis, activated carbon and ozonation have been shown to significantly reduce or eliminate antibiotics from wastewater effluents [32], The efficiency of two tertiary treatments, chlorination and UV disinfection, was compared and chlorination led to lower quantities of antibiotics [54],... 

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