Chlorine with carboxylate ions

Maeda, N., Ohya, T., Nojima. K.. and Kanno. S. Formation of cyanide ion or cyanogen chloride through the cleavage of aromatic rings by nitrous acid or chlorine. IX. On the reactions of chlorinated, nitrated, carboxylated or methylated benzene derivatives with hypochlorous acid in the presence of aimnonium ion, Chemosphere, 16(10-12) 2249-2258, 1987. 

Pyridine and quinoline /V-oxides react with phosphorus oxychloride or sulfuryl chloride to form mixtures of the corresponding a- and y-chloropyridines. The reaction sequence involves first formation of a nucleophilic complex (e.g. 270), then attack of chloride ions on this, followed by rearomatization (see also Section 3.2.3.12.5) involving the loss of the /V-oxide oxygen. Treatment of pyridazine 1-oxides with phosphorus oxychloride also results in an a-chlorination with respect to the /V-oxide groups with simultaneous deoxygenation. If the a-position is blocked substitution occurs at the y-position. Thionyl chloride chlorinates the nucleus of certain pyridine carboxylic acids, e.g. picolinic acid — (271), probably by a similar mechanism. 

Regarding ozonation processes, the treatment with ozone leads to halogen-free oxygenated compounds (except when bromide is present), mostly aldehydes, carboxylic acids, ketoacids, ketones, etc. [189]. The evolution of analytical techniques and their combined use have allowed some researchers to identify new ozone by-products. This is the case of the work of Richardson et al. [189,190] who combined mass spectrometry and infrared spectroscopy together with derivatization methods. These authors found numerous aldehydes, ketones, dicarbonyl compounds, carboxylic acids, aldo and keto acids, and nitriles from the ozonation of Mississippi River water with 2.7-3 mg L 1 of TOC and pH about 7.5. They also identified by-products from ozonated-chlorinated (with chlorine and chloramine) water. In these cases, they found haloalkanes, haloalkenes, halo aldehydes, haloketones, haloacids, brominated compounds due to the presence of bromide ion, etc. They observed a lower formation of halocompounds formed after ozone-chlorine or chloramine oxidations than after single chlorination or chlorami-nation, showing the beneficial effect of preozonation. 

The methoxide ion uses of its lone pairs of electrons to form a bond to the electrophilic carbonyl carbon of the acid chloride. Simultaneously, the relatively weak n bond of the carbonyl group breaks and both of the n electrons move onto the carbonyl oxygen to give it a third lone pair of electrons and a negative charge. This is exactly the same first step involved in nucleophilic addition to aldehydes and ketones. However, with an aldehyde or a ketone, the tetrahedral structure is the final product. With carboxylic acid derivatives, the lone pair of electrons on oxygen return to reform the carbonyl n bond (Step 2). As this happens, the C-Cl o bond breaks with both electrons moving onto the chlorine to form a chloride ion that departs the molecule. 

More recently, we have extended ion pairing to template-directed chlorination [15]. Since in the chlorination reactions HCl is produced, we could not use carboxyl-ate anions. However, ion pairs of substrate cations with iodoaryl templates carrying sulfonate anion groups directed chlorination with reasonably good selectivity. Somewhat poorer selectivity, because of flexibility, was achieved when the template carried the cationic group and the substrate was a sulfate anion. The ion paired template shows turnover catalysis by moving on to another substrate molecule after... 

The membrane process enables addition of hydrochloric acid into anolyte for neutralization of the OH ions, which enter through the membrane from catholyte (see Fig. 1). Moreover, anolyte can be acidified for reduced by-product formation. Oxygen evolution then is decreased to less than 0.5 vol.% in the anode gas and generation of hypochlorite and chlorate is completely suppressed (see reactions (3) and (5)-(7) in section 2 of entry Chlorine and Caustic Technology, Overview and Traditional Processes ). However, the addition of acid has to be performed very carefully with sufficient mixing of the anolyte, usually by the mammoth pump effect of the produced chlorine gas. The pH value must nowhere fall below 2. Otherwise, the carboxylic acid fixed ions (see upper part of Fig. 2), which are the anions of a relatively weak acid, will combine with H" ions and lose their activity so that the membrane is damaged. 

Wallach was the first (1874) to report on the transformation of carboxylic acid amides to amide chlorides by treatment with PCls various types of amides were converted by this reagent to chloromethyleneiminium chlorides (30 equation lg). - > Side reactions can include the a-chlorination of the amide chloride. If excess PCIs is used, the formation of iminium salts with complex ions (31) has been reported. The very labile bromomethyleneiminium bromides (32 equation 19) can be obtained by action of PBrs on tertiary amides. The iodomethyleneiminium salt (33) was prepared from DMF and diphosphorus tetraiodide in CS . ... 

The same process occurs with chlorine and iodine, and the by-products are chloroform and iodoform, respectively. This reaction is named after the by-product that is formed and is called the haloform reaction. The reaction must be followed by treatment with a proton source to protonate the carboxylate ion and form the carboxylic acid. This process is synthetically useful for converting methyl ketones into carboxyhc acids. 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives. Acyl halides can be a brominated or chlorinated by use of NBS or NCS and HBr or HCl. The latter is an ionic, not a free-radical halogenation (see 14-2). Direct iodination of carboxylic acids has been achieved with I2—Cu acetate in HOAc. " ° Acyl chlorides can be a iodinated with I2 and a trace of HI. Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium A-isopropylcyclohexylamide in THF and treatment of this solution at -78°C with... 

Treatment of either cis- or rrans-stilbene-2-carboxylic acids with chlorine or bromine leads to 4-halogeno-3,4-dihydro-3-phenylisocoumarins (58T<4)393). The reactions are stereospecific and are thought to involve intramolecular attack by the carboxyl group on a halonium ion. Ring closure to the corresponding 4-hydroxy compound also occurs stereo-specifically using peroxyphthalic acid (59JOC934). 

In addition to the monopolar membrane described above a large number of special property membranes are used in various applications such as low-fouling anion-exchange membranes used in certain wastewater treatment applications or composite membranes with a thin layer of weakly dissociated carboxylic acid groups on the surface used in the chlorine-alkaline production, and bipolar membranes composed of a laminate of an anion- and a cation-exchange layer used in the production of protons and hydroxide ions to convert a salt in the corresponding acids and bases. The preparation techniques are described in detail in numerous publications [13-15]. 

A carboxyl group usually hinders electrophilic attack. It is, therefore, at first sight surprising to note that picolinic acid hydrochloride reacts with thionyl chloride to give 4-chloropicolinic acid in yields of up to 55%.182-184 Under more severe conditions a 35% yield of 4,6-dichloropicolinic acid is obtained.182 Sulfur dioxide in the reaction mixture favors 4-chloropicolinic acid formation.183 This suggests that the chlorination may actually involve a nucleophilic attack by chloride ion upon a complexed pyridinium salt1 ... 

The behavior of chloromethyl esters of -carboxylic acids CH3(CH2) COOCH2Cl (n -2-12) and of all their 66 monochlorinated derivatives was examined with the aid of metastable linked scan techniques207. The main fragmentations were discussed with attention to the McLafferty rearrangement, which gives rise to abundant product ions for all compounds with n > 2 except for those in which the chlorine substituent occupies positions 3 and 5 in the chain. 

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