Hypochlorites

Hypochlorites - salts and esters of hypochlorous acid HClO.

Hypochlorites in a free anhydrous state are unstable compounds, many decompose upon heating with explosion. Hypochlorites of alkali and alkaline earth metals are readily soluble in water and form crystalline hydrates that decompose upon storage.

Content

Chemical Properties

Hypochlorites in aqueous solutions decompose, and the predominant direction of the decomposition reaction depends on pH and temperature.

In strongly acidic solutions (pH ≤ 3), in which hypochlorites are almost completely hydrolyzed and decomposition of hypochlorous acid to chlorine and oxygen predominates at room temperature:

{\mathsf {4HClO\rightarrow 2Cl_{2}+O_{2}+2H_{2}O}}

{\ displaystyle {\ mathsf {4HClO \ rightarrow 2Cl_ {2} + O_ {2} + 2H_ {2} O}}}

In slightly acidic and neutral solutions (pH 3-7.5) there is a reaction:

{\mathsf {2HClO\rightarrow 2HCl+O_{2}}}

{\ displaystyle {\ mathsf {2HClO \ rightarrow 2HCl + O_ {2}}}}

In a neutral environment, hypochlorites disproportionate to chlorides and chlorates , the reaction slowly proceeds even at room temperature and accelerates when heated, at temperatures above 70 ° C this reaction becomes predominant; this disproportionation is an industrial method of producing chlorates:

{\mathsf {3ClO^{-}\rightarrow ClO_{3}^{-}+2Cl^{-}}}

{\ displaystyle {\ mathsf {3ClO ^ {-} \ rightarrow ClO_ {3} ^ {-} + 2Cl ^ {-}}}}

Hypochlorites are strong oxidizing agents , and the oxidizing ability in a solution strongly depends on the pH of the medium. So, iodide ion at pH ≤ 4 is oxidized to free iodine I ₂ , at pH 5–7 - to iodate IO ₃ ^- , at pH ≥ 4 - to periodate IO ₄ ^- . Ions of transition metals in lower degrees of oxidation are often oxidized to higher degrees (for example, chromium salts are oxidized to chromates, manganese to permanganates).

Hypochlorites in an alkaline solution react with hydrogen peroxide to produce chloride and oxygen, a feature of this reaction is that oxygen is not released in the main triplet state, but in the excited singlet state, which determines its high activity and phosphorescence in the near IR range (~ 1270 nm):

{\mathsf {ClO^{-}+H_{2}O_{2}\rightarrow Cl^{-}+H_{2}O+^{1}O_{2}}}

{\ displaystyle {\ mathsf {ClO ^ {-} + H_ {2} O_ {2} \ rightarrow Cl ^ {-} + H_ {2} O + ^ {1} O_ {2}}}}

Hypochlorites interact with amines to form N-chloramines:

{\mathsf {R_{2}NH+OCl^{-}\rightarrow R_{2}NCl+OH^{-}}}

{\ displaystyle {\ mathsf {R_ {2} NH + OCl ^ {-} \ rightarrow R_ {2} NCl + OH ^ {-}}}}

The reaction with ammonia is similar; the interaction of excess ammonia with sodium hypochlorite under pressure (2.5-3.0 MPa 160 ° C) is used in the industrial production of hydrazine (Rashig process) ^[1] , the same method at atmospheric pressure is used for laboratory synthesis ^[2] :

{\mathsf {NH_{3}+NaOCl\rightarrow NH_{2}Cl+NaOH}}

{\ displaystyle {\ mathsf {NH_ {3} + NaOCl \ rightarrow NH_ {2} Cl + NaOH}}}

{\mathsf {NH_{2}Cl+NH_{3}+NaOH\rightarrow N_{2}H_{4}+NaCl+H_{2}O}}

{\ displaystyle {\ mathsf {NH_ {2} Cl + NH_ {3} + NaOH \ rightarrow N_ {2} H_ {4} + NaCl + H_ {2} O}}}

Organic Synthesis Application

The thermal or photochemical isomerization of alkyl hypochlorites is a method for the synthesis of δ-chloroalcohols (δ-chlorohydrins)
Hoffmann reaction : the interaction of carboxylic acid amides with hypochlorites leads to an intramolecular grouping into the corresponding isocyanates which, depending on the reaction conditions, can subsequently hydrolyze to primary amines or, in the presence of alcohols, form urethanes:

{\mathsf {RCONH_{2}+NaClO\rightarrow [RCONHCl+NaOH]\rightarrow RCNO+NaCl+H_{2}O}}

{\ displaystyle {\ mathsf {RCONH_ {2} + NaClO \ rightarrow [RCONHCl + NaOH] \ rightarrow RCNO + NaCl + H_ {2} O}}}

The reaction of hypochlorites with urea is one of the industrial methods for the synthesis of hydrazine:

{\mathsf {(NH_{2})_{2}CO+NaOCl+2NaOH\rightarrow N_{2}H_{4}+H_{2}O+NaCl+Na_{2}CO_{3}}}

{\ displaystyle {\ mathsf {(NH_ {2}) _ {2} CO + NaOCl + 2NaOH \ rightarrow N_ {2} H_ {4} + H_ {2} O + NaCl + Na_ {2} CO_ {3}} }}

The reaction of Schiff bases with alkyl hypochlorites leads to the formation of unstable N-chloro derivatives, rearranged into α-aminoketones
The interaction of amidines with hypohalogenites is used as a method for the synthesis of diazirines ^[3] , which are used in organic synthesis as carbene precursors ^[4] :

Oxidation of aromatic o-nitroamines to condensed furoxanes .

Industrial Applications

Historically, the first hypochlorite to find industrial application was potassium hypochlorite , which is part of the so-called. " Javelin water " ( French Eau de Javelle - a solution of hypochlorite and potassium chloride, obtained by passing chlorine through a solution of potash ), has been used to bleach cellulose tissue from the end of the XVIII century.

Sodium and calcium hypochlorites are large-capacity products; they are obtained by passing chlorine through a solution or suspension of the corresponding hydroxide with further crystallization of hypochlorite crystalline hydrate. A significant part of the hypochlorites produced by this method is used without isolation, that is, in a mixture with the corresponding chloride, for example, a mixture of hypochlorite and calcium chloride - bleach .

Due to the low cost and the fact that hypochlorites are strong oxidizing agents, they are used as a bleaching agent in the textile, paper, pulp industry, for the disinfection of drinking and waste water, etc., as well as as degassers of sulfur-containing and organophosphorus poisonous substances.

Biological Importance

The hypochlorite anion is formed during the oxidation of the chloride anion, catalyzed by the myeloperoxidase of neutrophilic granulocytes and, as one of the biocidal factors (the so-called active forms of oxygen), is involved in protecting the body from bacterial and fungal infections. So, in particular, in addition to the direct cytotoxic effect, the interaction of hypochlorite with hydrogen peroxide leads to the release of oxygen in a highly toxic singlet state :

{\mathsf {ClO^{-}+H_{2}O_{2}\rightarrow Cl^{-}+H_{2}O+^{1}O_{2}}}

{\ displaystyle {\ mathsf {ClO ^ {-} + H_ {2} O_ {2} \ rightarrow Cl ^ {-} + H_ {2} O + ^ {1} O_ {2}}}}

Notes

↑ Schirmann, Jean-Pierre & Bourdauducq, Paul (2001), "Hydrazine" , Ullmann's Encyclopedia of Industrial Chemistry , DOI 10.1002 / 14356007.a13_177
↑ Adams, R. & Brown, BK (1941), " Hydrazine Sulfate ", Org. Synth. , < http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0309 > ; Coll. Vol. T. 1: 309
↑ Graham, WH The Halogenation of Amidines. I. Synthesis of 3-Halo- and Other Negatively Substituted Diazirines1 (Eng.) // Journal of the American Chemical Society : journal. - 1965. - 1 October ( vol. 87 , no. 19 ). - P. 4396-4397 . - ISSN 0002-7863 . - DOI : 10.1021 / ja00947a040 .
↑ Albert Padwa; Mitchell J. Pulwer & Thomas J. Blacklock (1981), " Preparation of chlorophenyldiazirine and thermal generation of chlorophenyl carbene: 1,2-diphenyl-3-methylcyclopropene ", Org. Synth. , < http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV7P0203 > ; Coll. Vol. T. 60: 53

Literature

Knunyants I.L. et al. 1 A-Darzan // Chemical Encyclopedia. - M .: Soviet Encyclopedia, 1988 .-- 623 p. - 100,000 copies.

[1] Schirmann, Jean-Pierre & Bourdauducq, Paul (2001), "Hydrazine" , Ullmann's Encyclopedia of Industrial Chemistry , DOI 10.1002 / 14356007.a13_177

[2] Adams, R. & Brown, BK (1941), " Hydrazine Sulfate ", Org. Synth. , < http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0309 > ; Coll. Vol. T. 1: 309

[3] Graham, WH The Halogenation of Amidines. I. Synthesis of 3-Halo- and Other Negatively Substituted Diazirines1 (Eng.) // Journal of the American Chemical Society : journal. - 1965. - 1 October ( vol. 87 , no. 19 ). - P. 4396-4397 . - ISSN 0002-7863 . - DOI : 10.1021 / ja00947a040 .

[4] Albert Padwa; Mitchell J. Pulwer & Thomas J. Blacklock (1981), " Preparation of chlorophenyldiazirine and thermal generation of chlorophenyl carbene: 1,2-diphenyl-3-methylcyclopropene ", Org. Synth. , < http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV7P0203 > ; Coll. Vol. T. 60: 53