Condensation hydrogen halides

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

Removal of the 2 -sulfonyloxy group of 859 in a basic medium, followed by reaction with metal halides (LiBr and Nal) or hydrogen halides (HCl-1,4-dioxane, HBr-acetone, or0.1% HFin l,4-dioxane-AlF3)gave, byway of the 2,2 -anhydro intermediate 861, the 2 -halo derivatives 862-865. The 2 -deoxy analog 866 and l-(6-deoxy-6-fluoro- ff-D-mannopyranosyl)thy-mine were also prepared from 864 (R = H) and 861 (R = H), respectively. l-(4-Deoxy-4-fluoro-y -D-glucopyranosyl)thymine was obtained by the condensation method. A different kind of nucleoside, 5-(5-deoxy-5-fluoro-2,3-0-isopropylidene-a-D-ribofuranosyl)-l,3-dimethyluracil has also been prepared. ... 

The imide nitrogen atom was also most reactive to a variety of electrophilic species (hydrogen halides, pseudohalogens, and alkyl halides) in the parent Rimidophosphazenes, R(C—NH)-N=PPh3. With t-butyl hypochlorite the /V-chloro-derivatives, R(C=NCl)-N=PPh3, were obtained. R/ -Vinyl-phenylphosphazenes have been prepared by condensation of aldehydes with active methylene compounds ... 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

In order to find out what R+ is, we consider first the common experience that when a tert- mty halide is treated with an aluminium halide under ordinary conditions, there is a brisk evolution of hydrogen halide and a coloured solution containing oligo-isobutylenes and condensed allylic ions is formed. In the present experiments the solutions were colourless, no hydrogen halide was evolved, and the conductivity was stable and behaved reversibly. Further, the rectilinearity of the k-[A1X3] plots in Figures 9 and 10, and the smallness of the intercepts on the K-axis, showed that ions generated by reactions other than those of type (viii) must have been very scarce, and for the experiment with tert-butyl bromide this was borne out by the absence of any byproducts. 

Figure 6.15. The apparatus of Schnepf and Schnockel (2002) for the preparation and co-condensation of A1 (or Ga) mono-halide. 1 stainless steel vessel, 30/ 2 solvent input LM/D 3 drainage channel 4 A1 in the graphite cell with resistance heating 5 cooling shield 6 Dewar with dry ice (—78°C) 7 cooling water. HX hydrogen halide gas HV high vacuum.

Dipo/e Moment The evidence comes from an examination of the dielectric constant of the hydrogen halides. In an electric field, say between the plates of a condenser, molecules that have a charge separation within them will tend to orient themselves with the electric field. Such molecules behave like electric dipoles (Fig. 4.3) and are called polar molecules. The extent of orientation is reflected by a change in the dielectric... 

Zinc is frequently used for bringing about condensation by the elimination of halogen or of hydrogen halide. 

In contrast to the condensation described above (Section II, A, 1) which proceeds vigorously because of continuous evolution of hydrogen halide, the methylmercapto compounds can be condensed with excess of methyl derivatives of N heterocycles in a slow and mild reaction16,17 Eq. (2) formulates this reaction for di-(2-quinolyl)-methane. 

The reaction of atomic carbon with A -methylpyrrole 1020 at 77 K generates the A -methyl-3-dehydropyridinium ylide 1021, novel reactive intermediate (Scheme 198), which can be trapped with added hydrogen halides or carbon dioxide <1997JA5091>. The intermediacy of ylide 1021 in the 77 K cocondensation of arc generated carbon with pyrrole 1020 is implied by the fact that addition of methanolic HCl to the cold condensate generates the A -methylpyridinium ion 1023. 

Examples include pyrolysis of an alkylbenzene homogeneous aldehyde hydrogenation olefin hydroformylation to alcohol with paraffin by-product formation, aldehyde condensation to heavy ends, and olefin isomerization cyclo-addition reactions and hydrogen-halide reactions. 

An aluminum reactor, fitted with a Hg seal stirrer, dropping funnel and reflux condenser connected to two traps cooled at 0 C and —78 C, respectively, was charged with powdered SbF, (635 g. 3.54 mol) and SbF,CL (718 g, 2.87 mol). The vessel was cooled with ice and CHXI, (950 mL.) was added slowly once the addition was complete, 1.1,1,3-tctrachloropropanc (3 910 g, 5.0 mol) was added over a period of 3 h with cooling. Only very small amounts of hydrogen halides were evolved and only a small amount of CH, F, (50-70g) was collected in the dry ice trap. After completion of the addition, the mixture was stirred for a further 2 h and then coned HC1 (.50 mL) was added and the mixture was steam-distilled. The lower layer of the distillate was decanted, dried (CaCI2) and distilled to give 4 yield 530 g (80%) bp 45 C. 

The dehydrohalogenation of a yQ-chloroalkylbenzene is readily accomplished by refluxing with excess aqueous methanolic potassium hydroxide. Substituted a-alkylstyrenes which are difficult to obtain by other methods are prepared in this way by a two-step process involving catalytic condensation of aromatic compounds with aliphatic chlorohydrins followed by removal of hydrogen halide from the resulting haloalkylated derivatives. ... 

Olefins, addition—Continued of diazoacetic ester, 498 of halo ethers, 232 of halogen, 106 of hydrogen cyanide, 603 of hydrogen halide, 105 of hypohalous acid, 109 of polyhalides, 107 to cyanides, 571 allylic bromination, 36, 104 condensation, with halides, 108 with phenols, 179 conversion to amides (Wi 11 gerodt),... 

Oftentimes condensation reactions are promoted by the liberated hydrogen halide (cf. method 36). This difficulty may be overcome by bro-minating in the presence of calcium carbonate or potassium chlorate. ... 

All hydrogen halide samples are purified before use HCl, HBr, HI (Matheson Gas Products), and DCl (Merck) are condensed at 77 K, pumped on, and then distilled to remove parent halogen impurities HF (Matheson), which is handled in a copper vacuum line fitted with Monel valves, is condensed at 196 K and pumped on to remove SiF. ... 

By far the most important type of reaction displayed by halophosphines is nucleophilic substitution. This is pivotal to the preparation of many other three-coordinate compounds containing either solely P—C, P—O, P—N bonds, or mixed combinations. These reactions are often exothermic and frequently carried out at low temperatures. For the synthesis of phosphorus(III) compounds containing a P—O or P—N bond it is often necessary to add a base (triethylamine or pyridine are frequently used) to capture the hydrogen halide eliminated from these condensation reactions. In the case of P—C bond formation, a variety of routes are possible using various carbon-derived nucleophiles. 

Besides the addition of such reagents as halogens, hydrogen halides, or the hypohalous acids, there are other reactions which appear to proceed through addition mechanisms, but the exact course of the process is sometimes considerably obscured. The Friedel-Crafts addition of alkyl halides to olefins (p. 145), the self-condensation of olefins, and the alkylation of isoparaffins are examples in which attack at the double bond seems to be led by a carbonium ion. 

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