Picric acid chlorination

For phenols, the number of chlorines replaced depends in part on the acidity of the phenol. Under mild conditions, phenol or y -nitrophenol displaces only one chlorine from TiCl, whereas -chlorophenol, (9-nitrophenol, -nitrophenol, picric acid, or 2-naphthol gives (ArO)2TiCl2. If the mixtures are heated sufficiently, eg, in refluxing phenol, all four chlorines can be displaced (49—52). 

CC13 N02 +3C02 +6H2 0+2HC1 When reacted with chlorine, aqua regia or K chlorate in the presence of HCi, Picric Acid yields chloranil along with chloropicrin ... 

Cl Sulphur Black 1, which is produced from the relatively simple intermediate 2,4-dinitrophenol and aqueous sodium polysulphide. A similar product (Cl Sulphur Black 2) is obtained from a mixture of 2,4-dinitrophenol and either picric acid (6.148 X = N02) or picramic acid (6.148 X = NH2). A black dye possessing superior fastness to chlorine when on the fibre (Cl Sulphur Black 11) can be made from the naphthalene intermediate 6.149 by heating it in a solution of sodium polysulphide in butanol. An equivalent reaction using the carbazole intermediate 6.150 gives rise to the reddish blue Cl Vat Blue 43 (Hydron blue). This important compound, which also possesses superior fastness properties, is classified as a sulphurised vat dye because it is normally applied from an alkaline sodium dithionite bath. Interestingly, inclusion of copper(II) sulphate in the sulphurisation of intermediate 6.150 leads to the formation of the bluish black Cl Sulphur Black 4. 

Acetone, Sulfuric acid. Chlorine, Calcium chloride Triethylamine, Acetonitrile, Methylenedinitramine, 4,5-Dichloro-l,3-dioxolan-2-one. Silica gel. Benzene, Ethanol Picric acid. Sulfur, Potassium nitrate. Sulfuric acid. Sodium hydroxide... 

Reactions. -Hydroxybenzoic acid undergoes the typical reactions of the carboxyl and hydroxyl moieties. When heated above its melting point, it decomposes almost completely into phenol and carbon dioxide. It reacts with electrophilic reagents in the predicted manner and does not undergo the Friedel-Crafts reaction. Nitration, halogenation, and sulfonation afford the 3-substituted products. Heating -hydroxybenzoic acid with 8 IV-nitric acid results in a 95% yield of picric acid. In a similar fashion, treatment with chlorine water yields 2,4,6-trichlorophenol (50). 

The reaction was first observed by Stenhouse [146] in 1847, when treating picric acid with a hypochlorite. According to A. W. Hofmann [147], a 114 wt. % yield could be obtained in the reaction. As Gardner and Fox [148] reported, the yield could be increased up to 180 - 190%. A yield of chloropicrin amounting to about 200% can be obtained by introducing gaseous chlorine into a suspension of sodium picrate in a solution of sodium carbonate at 0°C (Orton and McKie [149]). 

Chemical properties. The chlorine atom in a picryl chloride molecule is exceptionally reactive. Besides hydrolysis to picric acid when heated with water, as mentioned above, picryl chloride can yield picric acid when boiled with alcohols, according to the equation ... 

Hypochlorites decompose picric acid, which undergoes chlorination to form chloropicrin. The reaction is carried out with calcium hypochlorite. The calcium hydroxide formed in the reaction neutralizes the hydrochloric acid formed. This is a commercial method of preparation of chloropicrin. 

Technical Observations. Dinitrochlorobenzene is manufactured on a very large scale, and is used in the preparation of sulfur black T (q.v.) and other important dyes. It is, moreover, the starting material for a whole series of condensation products made by replacing the very labile chlorine atom by basic and other residues. Thus, it is easy to prepare dinitroaniline and dinitrophenol, as well as picric acid and dinitroanisole, from dinitrochlorobenzene. The accompanying formulas show only a small part of the reactions actually used (also see Table V). 

According to a patent by Orton and Pope, chloropicrin may also be obtained by the direct action of chlorine on picric acid, or other nitro-derivative of phenol or of naphthol ... 

The reaction is carried out in alkaline solution (sodium or potassium hydroxide, or a mixture of the corresponding carbonates) so as to dissolve the nitro-compound and to neutralise the hydrochloric acid which otherwise impedes the chlorination of the picric acid. The reaction takes place very readily at a low temperature (between o and 5° C.). 

Chlorination. The reagent can function as a chlorinating agent. Thus picric acid is converted into picryl chloride, and the 1,3,5-triazine (1) yields the corresponding dichloro compound (2). ... 

The reagent is obtained in high yield by passing chlorine into a well-cooled mixture of picric acid and calcium hydroxide. The product is separated by steam distillation, dried, and distilled. 

Derivation (1) Action of picric acid on calcium hypochlorite (2) nitrification of chlorinated hydrocarbons. 

Chemistry Chloropicrin s first reported preparation, by the Scottish scientist John Stenhouse, was in 1848 and involved the reaction of a chlorinating agent (bleaching powder) with picric acid (iym-trinitrophenol). It is this synthesis that led to the name chloropicrin, even though the ring present in picric acid is absent in the product chloropicrin. 

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