P-Halide compounds

This section is concerned mostly with the enzymatic hydrolysis of substrates classified as phosphoric acid mono-, di-, and triesters, phosphonates, phosphoro(di)thioates, phosphonodithioates, and P-halide compounds. 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

Aldehydes, formates, primary, and secondary alcohols, amines, ethers, alkyl halides, compounds of the type Z—CH2—Z, and a few other compounds add to double bonds in the presence of free-radical initiators/ This is formally the addition of RH to a double bond, but the R is not just any carbon but one connected to an oxygen or a nitrogen, a halogen, or to two Z groups (defined as on p. 548). The addition of aldehydes is illustrated above. Formates and formamides " add similarly ... 

Fig. 8. Correlation between Pearson s hardness parameter (7P) derived from gas-phase enthalpies of formation of halide compounds of Lewis acids (19), and the hardness parameter in aqueous solution (/A), derived from formation constants of fluoride and hydroxide complexes in aqueous solution (17). The Lewis acids are segregated by charge into separate correlations for monopositive ( ), dipositive (O), and tripositive ( ) cations, with a single tetrapositive ion (Zr4+, ). The /P value for Tl3+ was not reported, but the point is included in parentheses to show the relative ionicity of Tl(III) to ligand bonds. 

Main-group elements X such as monovalent F, divalent O, and trivalent N are expected to form families of transition-metal compounds MX (M—F fluorides, M=0 oxides, M=N nitrides) that are analogous to the corresponding p-block compounds. In this section we wish to compare the geometries and NBO descriptors of transition-metal halides, oxides, and nitrides briefly with the isovalent hydrocarbon species (that is, we compare fluorides with hydrides or alkyls, oxides with alkylidenes, and nitrides with alkylidynes). However, these substitutions also bring in other important electronic variations whose effects will now be considered. 

Alkylation of P-dicarbonyl compounds and p-keto esters occurs preferentially on the carbon atom, whereas acylation produces the 0-acyl derivatives (see Chapter 3). There are indications that C- and 0-alkylated products are produced with simple haloalkanes and benzyl halides, but only C-alkylated derivatives are formed with propargyl and allyl halides [e.g. 90]. Di-C-alkylation frequently occurs and it has been reported that the use of tetra-alkylammonium 2-oxopyrrolidinyl salts are more effective catalysts (in place of aqueous sodium hydroxide and quaternary ammonium salt) for selective (-90%) mono-C-alkylation of p-dicarbonyl compounds [91]. 

The glycosyl halide (1.5 mmol), p-dicarbonyl compound (2 mmol), anhydrous K3P04 (0.S5 g) and TBA-Br (24 mg, 0.075 mmol) in McCN (10 ml) are stirred at room temperature. When the reaction is complete, as indicated by TLC analysis, the mixture is filtered and evaporated to yield the C-glycosyl derivative. 

The toxicity of the P-halidc anhydrides, like that of phosphoroxychloride (POCl3) and of other organophosphorus compounds discussed earlier in this section, is due to their high efficiency as irreversible inactivators of acetylcholinesterase [157]. The main target organs for the lethal effects of these chemical weapons are the brain and diaphragm. As for the detoxification of the P-halide anhydrides, it can occur by a number of biochemical mechanisms, namely chemical hydrolysis, enzymatic hydrolysis, and binding to hydrolases such as carboxylesterases, cholinesterases, and albumin [68][158][159]. 

UNSATURATED p-DICARBONYL COMPOUNDS Benzeneselenenyl halides. Selenium. 

Even at the inception of ALPH, however, there was one system already known where the pattern of reactivity apparently contradicted it. It was well known in carbohydrate chemistry that protected a-glycopyranosyl halides were less labile than their p-anomers, at least for the common sugars in the D series (Haynes and Newth, 1955). The pyranose ring in these compounds is strongly biased towards the 4CX conformation, so that the a-halides are axial and the P-halides are equatorial. The a-halides have an antiperiplanar... 

In the vast majority of cases in which six coordination is observed, the bonding can be viewed as arising from the interaction of all three cr -orbitals with a halide anion, i.e., all three in S. Because the three orbitals are all trans to the primary E-X bonds, such a situation leads naturally to octahedral coordination. Moreover, in cases in which the primary and secondary bonds are the same length, i.e., where A = 0 and a three-center, four-electron bonding model is appropriate, a regular octahedron is the result. Such a structure is clearly at odds with simple VSEPR theory, which is predicated on the lone pair(s) occupying specific stereochemical sites, but stereochemical inactivity of the lone pair tends to be the rule rather than the exception in six-coordinate, seven-electron pair systems Ng and Zuckerman (102) have reviewed this topic for p-block compounds in general. 

The heteroatom cross-coupling reaction of N-H, 0-H, S-H and P-H compounds is a topic of current interest. Alkenyl halides were converted into the... 

The protonolysis reaction tolerates functionalities such as halide or ether groups in the alkylborane. However, p-dialkylaminoalkylboron compounds undergo elimination to give alkenes under these conditions (see Section 3.10.1.2). ° " Also, systems which are intrinsically labile to either acid or heat, such as some terpenoids, may give problems. For example, enantiomerically pure limonene produces 1 -men-thene which is substantially racemized on hydroboration-protonolysis (Scheme 15). 

SbCU molybdenum pentachloride, MoCU iodine, sulphur, phosphorus or metallic iron, the last four forming first their respective halide compounds. The organic compound pyridine (p. 858), may also be used. In this way chlorine or bromine may be introduced into the benzene ring atom by atom until all six hydrogens are substituted as follows ... 

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