Complex hydrogen halides

Blake and Kubota have convincingly shown that in anhydrous benzene, chloroform and ether, as in the gaseous reaction on the solid complex, hydrogen halides (HX) and /m -[Iry(CO)(PPh3)2] (T = halogen) react to give octahedral cw-addition products (i.e. H and X cis). In contrast in wet solvents, and in such solvents as dimethylformamide, acetonitrile and ethanol, mixtures of cis and trans products are formed. Whether these solvents cause rapid halide-ion exchange before the addition reaction or in the products is yet to be demonstrated. ... 

As well as the cr-complexes discussed above, aromatic molecules combine with such compounds as quinones, polynitro-aromatics and tetra-cyanoethylene to give more loosely bound structures called charge-transfer complexes. Closely related to these, but usually known as Tt-complexes, are the associations formed by aromatic compounds and halogens, hydrogen halides, silver ions and other electrophiles. 

A number of complex bismuth halides are weU-known, eg, disodium bismuth pentachloride [66184-10-9] Na2BiCl sodium dibismuth heptachloride [66184-09-6J, NaBi Cl and trisodium bismuth hexachlotide [66114-82-7J, Na BiCl. The acid, hydrogen dibismuth heptachloride tnhydrate [66124-39-9] HBi Cl 3H20, is a crystalline substance, stable at room temperature, that maybe isolated by cooling a solution of BiCl in concentrated hydrochloric acid to 0°C. 

The use of fire retardants in polymers has become more complicated with the realisation that more deaths are probably caused by smoke and toxic combustion products than by fire itself. The suppression of a fire by the use of fire retardants may well result in smouldering and the production of smoke, rather than complete combustion with little smoke evolution. Furthermore, whilst complete combustion of organic materials leads to the formation of simple molecules such as CO2, H2O, N2, SO2 and hydrogen halides, incomplete combustion leads to the production of more complex and noxious materials as well as the simple structured but highly poisonous hydrogen cyanide and carbon monoxide. 

The order of reactivity of the hydrogen halides is HI > HBr > HCl, and reactions of simple alkenes with HCl are quite slow. The studies that have been applied to determining mechanistic details of hydrogen halide addition to alkenes have focused on the kinetics and stereochemistry of the reaction and on the effect of added nucleophiles. The kinetic studies often reveal complex rate expressions which demonstrate that more than one process contributes to the overall reaction rate. For addition of hydrogen bromide or Itydrogen... 

The third-order process presumably involves reaction of a complex formed between the alkene and hydrogen halide with the second hydrogen halide molecule, since there is little likelihood of productive termolecular collisions. 

These reactions give products similar to those described in 8.3.2.1. Transition-mclal hydrido complexes react with a halogen derivative of a group-IB metal to form a hydrogen halide and the required metal-metal bond ... 

The stereochemistry of addition depends on the details of the mechanism. The addition can proceed through an ion pair intermediate formed by an initial protonation step. Most alkenes, however, react via a complex that involves the alkene, hydrogen halide, and a third species that delivers the nucleophilic halide. This termolecular mechanism is generally pictured as a nucleophilic attack on an alkene-hydrogen halide complex. This mechanism bypasses a discrete carbocation and exhibits a preference for anti addition. 

In order to elucidate the causes of the increased stability of the hydrolyzed cluster ions compared with the unhydrolyzed ions, further studies were made of the behaviour of [Te2X8]3 (where X = Cl,Br, or I) in solutions of hydrogen halides [43,52,80,87]. The studies were performed mainly in relation to the most stable and most readily synthesized [Tc2C18]3- ion (Fig. la) kinetic methods with optical recording were employed. The identity of the reaction products was in most cases confirmed by their isolation in the solid phase. The studies showed that the stability of the [Tc2X8]3 ions (where X = Cl, Br, or I) in aqueous solutions is determined by the sum of competing processes acid hydrolysis complex formation with subsequent disproportionation and dissociation of the M-M bonds, and oxidative addition of atmospheric oxygen to the Tc-Tc multiple bond. 

The dihaptoformaldehyde complex 0s(Tj2-CH20)(C0)2(PPh3)2 reacts with hydrogen halides, affording hydroxymethyl species. Further reaction leads to the formation of halomethyl complexes, probably via the intermediacy of methylene complexes (60) (73) ... 

This is a widely used preparation route towards metal chalcogenolates since the alkali compounds, mainly lithium and sodium derivatives, react with halogen complexes of almost any metal. The chalcogenols in the presence of a base can be used to scavenge the hydrogen halide. 

This type of hydrodehalogenation has been performed generally in the presence of organic or inorganic bases to neutralize the hydrogen halides formed. Among published results, the use of rhodium complexes as catalysts dominates, but palladium and ruthenium complexes have also been applied on a frequent basis. 

We use the term conventional acid to designate stable acids such as the hydrogen halides and the common mineral and organic acids, in order to distinguish them from the complex acids such as the hydrates of metal halides and the adducts formed from, for example, trichloroacetic acid and titanium tetrachloride. 

An incorrect statement to the effect that there is no evidence for the complexing of double bonds with hydrogen halides must be corrected. This writer himself has quoted several times the demonstration by O. Maas and his collaborators that the HX (X = Cl, Br) do form complexes with alkenes [A, B],... 

Class I is covered by the current theory. The Class II reactions can be explained on the assumption that although the acids HMXn+1 have no independent existence, HX can react with the olefin-MX complex to give a carbonium ion and MXn+1. Since the halides of B, Ti and Sn form complexes neither with a double bond nor with the hydrogen halide, the latter cannot be expected to act as co-catalyst in the polymerization of alkenes. 

In the ternary systems aromatic substance (A)-Lewis acid (MX3)-hydrogen halide (HX) the formation of a proton addition complex can be formulated analogously. 

Assignments for the ternary complex benzene-Lewis acid-hydrogen halide (Perkampus and Baumgarten, 1963a)... 

The complex formation of aromatic hydrocarbons with Lewis acids in the presence of hydrogen halide and the colour of the so-called red oils associated with this is the oldest observation which indicates that the interaction is connected with a pronounced effect on the electronic structure of the aromatic hydrocarbons (Gustavson, 1878, 1890, 1903, 1905). 

The halide catalysts are electron acceptors, and, in the absence of hydrogen halide promoter, the active complex is presumably formed by the addition of the catalyst to the olefin (Hunter and Yohe, 17 cf. Whitmore, 18) ... 

The polymerization of olefins in the presence of halides such as aluminum chloride and boron fluoride but in the absence of hydrogen halide promoter may also be described in terms of the complex carbonium ion formed by addition of the metal halide (without hydrogen chloride or hydrogen fluoride) to the olefin (cf. p. 28). These carbonium ions are apparently more stable than those of the purely hydrocarbon type the reaction resulting in their formation is less readily reversed than is that of the addition of a proton to an olefin (Whitmore, 18). Polymerization in the presence of such a complex catalyst, may be indicated as follows (cf. Hunter and Yohe, 17) ... 

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