Hydrogen chloride heterogeneous reactions

Abstract Heterogeneous chemical reactions at the surface of ice and other stratospheric aerosols are now appreciated to play a critical role in atmospheric ozone depletion. A brief summary of our theoretical work on the reaction of chlorine nitrate and hydrogen chloride on ice is given to highlight the characteristics of such heterogeneous mechanisms and to emphasize the special challenges involved in the realistic theoretical treatment of such reactions. 

Horn, A. B., J. R. Sodeau, T. B. Roddis, and N. A. Williams, Mechanism of the Heterogeneous Reaction of Hydrogen Chloride with Chlorine Nitrate and Hypochlorous Acid on Water Ice, J. Phys. Chem. A, 102, 6107-6120(1998). 

Theoretical and experimental studies of the interactions between water molecules and hydrogen chloride are of fundamental importance for the understanding of the production of stratospheric chlorine molecules which, in turn, take part in the catalytic ozone depletion reactions. This mainly heterogeneous atmospheric reaction begins with the adsorption of the HCl molecules on the surface of water icicles is the source of the stratospheric chlorine atoms in the polar regions380 - 382. Chlorine molecules are photolysed by solar radiation and the resultant chlorine atoms take part in the destruction of the stratospheric ozone. The study of the (H20) HC1 clusters is an important step towards understanding of the behavior of the HCl molecule on the ice surface383- 386. 

Chu LT, Leu MT, Keyser LF (1993) Heterogeneous reactions of hypochlorous acid + hydrogen chloride - Cl2 + H20 and chlorosyl nitrite + HC1 — Cl2 + HNOs on ice surfaces at polar stratospheric conditions. J Phys Chem 97 12798—12804... 

No vigorous, exothermic reaction is seen during the addition of acetyl chloride, but the additon should be slow because of the heterogeneous nature of the reaction and the need to destroy efficiently hydrogen chloride as it is formed. The product, like N-phenyl hydroxyl amine. Is sensitive to... 

The direct, copper catalyzed reaction of methyl chlorid with silicon, the Direct Process , is the most important reaction for the production of methylsilicon intermediates. A similar reaction with hydrogen chloride yields trichlorosilane, which in turn is the basis for trifiinctional intermediates and also for polycrystalline silicon, the raw material for the semiconductor industry. This Direct Process has been practiced for fifty years and much progress has been made by many towards understanding and optimizing the process, but much still remains to be learned about this complex series of heterogeneous reactions. 

Up to the early 1980s VCM was produced by addition of hydrogen chloride to acetylene. In this process the gaseous reactants are brought into contact with the catalyst at slightly increased pressure and 100-250 °C [1]. Mercury(II) chloride on activated carbon is used as a catalyst in this heterogeneous process. Today, however, this reaction has no economical importance. Nowadays, VCM is exclusively produced by thermal decomposition of DCE. 

Of more interest mechanistically though is the liquid nature of the molten phase present in the interstices of the inert porous support. It is now recognized that, deliberately or accidentally, a number of heterogeneously catalysed processes involve a supported liquid phase (SLP) rather than a solid catalyst. SLP catalysts are reviewed by Villadsen and Livbjerg. These include the vanadium-based sulphuric acid catalysts and, of comparable antiquity, the Deacon catalysts for oxidizing hydrogen chloride, where mixtures of copper and potassium chlorides can form melts in the catalyst support under reaction conditions. Thus in addition to diflfusional restrictions arising from pellet pore structure any... 

The heterogeneously catalysed conversion of eth3me (acetylene) into vinyl chloride (chloroethene) by the addition of hydrogen chloride is a reaction important for the manufacture of pol3rvinyl chloride (PVC) [18, 213, 248, 249]. Mercuric chloride, supported on activated carbon, is often used as a catalyst commercially [18, 213, 248-252] but, unfortunately, this catalyst rapidly deactivates. The high rate of deactivation, together with the toxicity associated with mercury compounds, has prompted a search for alternative catalysts [213,248,249,251,252]. 

It is known that the chlorination of ethane with chlorine formed in the oxidation of hydrogen chloride proceeds by a heterogeneous—homogeneous mechanism [3]. This is why the effieiency of cement catalysts was studied separately by the examples of Deacon reaction and dichloroethane dehydrochlorination reaction. 

Many other important reactions involve reactants in two phases. These reactions are heterogeneous reactions. An example of a heterogeneous reaction is zinc metal reacting with hydrochloric acid to produce hydrogen gas and aqueous zinc chloride ... 

Reduction of carboxylic acids to aldehydes Replacement of the Rosenmund reaction (conversion of carboxylic acids to acid chlorides followed by catalytic hydrogenation) or the reaction of Grignard reagents with formic esters by molecular hydrogen and heterogeneous catalysts (Ru3Sn7 alloy). 

Leu, M.-T., Moore, S.B., Keyser, L.L. Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds. J. Phys. Chem. 95, 7763-7771 (1991)... 

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