Reduction halogen-free

The heptanuclear iron carbonyl cluster [Fe3(CO)u(/u-H)]2-Fe(DMF)4 (178) acted as an efficient catalyst in the reduction of carboxamides by l,2-bis(dimethylsilyl)benzene in toluene to the corresponding amines in high yields. Several tertiary and secondary amides including a sterically crowded amide were also reduced smoothly A review of the development of optically active cobalt complex catalysts for enan-tioselective synthetic reactions has addressed the applications of ketoiminatocobalt(II) complexes such as (5)-MPAC (179) and (5)-AMAC (180), transition-state models for borohydride reduction, halogen-free reduction by cobalt-carbene complexes. 

It is not possible to use zinc for reductive debromination in the presence of (x-halo ketones and for transformations involving these intermediates, sodium iodide has been used. ° In some instances, e.g. 5,6-dihalo-3-ketones, iodide does not always give a completely halogen-free product, and zinc does not give clean debromination. The use of chromous chloride has proved advantageous in such cases and is the reagent of choice for vicinal dichlorides, which are inert to iodide ... 

Research has focused on improving the efficiency of the halogenation-oxidation-reduction route by using reagents that perform the halogenation-oxidation in one step. Hypochlorous acid-hypochlorite and hypobromous acid-hypobromite " systems have also been explored for the direct conversion of oximes to a-bromonitroalkanes and a-chloronitroalkanes respectively. Some A-haloheterocycles have been reported to affect direct oxime to a-halonitroalkane conversion, and on some occasions, the use of NBS or the free halogens also leads to a-halonitroalkanes. A mixture of oxone and sodium chloride as a suspension in chloroform is reported as a one-pot method for the direct conversion of oximes to a-chloronitroalkanes. ... 

The biochemical reduction of a, -unsaturated -haloaliphatic acids by means of Clostridium kluyveri yielded halogen-free satmated acids. The same products were obtained from saturated -halo acids. However, the same microorganism converted ix, -unsaturated a-halo acids to saturated a-halo acids with R configuration. Yields of reduction of a-fluoro-, a-chloro- and a-bromocrotonic acid ranged from 30% to 100% [330]. 

Reduction of oj.-bromoacetophenone gave the corresponding bromo-hydrin in 85% yield.6 Smooth reduction, also occurred with chloral2-16 and bromal.6 However, a-bromopropiophenone 44 gave only 35 to 42% yields of the bromohydrin the remainder of the product was halogen-free, consisting of a mixture of benzylmethylcarbinol and some ethers. 

In catalytic hydrogenation, chlorine is replaced by hydrogen in chlorinated aromatic hydrocarbons (equations 41 and 42), phenols (equation 43), amines (equation 44), carboxylic acids (equation 45), and nitro compounds (equation 46). - Hydrogenolysis of chlorine in chloronitro compounds takes precedence over reduction of nitro groups, provided that contact with the halogen-free product is not too long. The reaction is achieved using palladium on carbon or tetrakis(triphenylphos-... 

Speyer and Rosenfeld on reduction of 14-bromocodeinone [xxn] with sodium hydrosulphite obtained an amorphous halogen-free base that was converted by hot alkali to a crystalline, ketonic, tertiary base Cx8H2i03N that they suggested was dihydro-i/ -codeinone [40], but its properties do not agree with those of the latter [7] and its nature remains obscure. 

Another general theme in product development will be the reduction of secondary products (100 % conversion) or their utilization. What the chemical engineers will be looking for will be polymer formulae that produce migration-free, halogen-free, reusable products (additives free of heavy metals). 

Another trend in many applications is towards halogen-free products or at least to combinations which will permit a reduction in the percentage of halogen. Japanese patents have opened up the market for melamine compounds that can also be used in combination with other FRs such as magnesium hydroxide or even a filler like talc. 

Joseph Storey has introduced a zinc hydroxystannate flame retardant, which it found to be the closest non-toxic alternative to antimony trioxide in halogenated systems. The new material also has excellent smoke suppression properties. In halogen-free systems, tin char formation occurs, leading to reductions in filler loadings and improved physical properties. 

Epoxy resins can be made flame retardant with reactive halogen-free FRs attached to the polymer matrix. To achieve this the compounds must be miscible with commercial epoxy resins. Schill Seilacher Struktol of Hamburg offer just such a material. Their reactive organophosphoms compoimd Struktol Polydis PD3710 can produce UL94 V-0 with 2-4% phosphoms in the polymer matrix. At the same time, a reduction in smoke density is achieved. 

The reduction of smoke obscuration and corrosivity favour this group of flame-retardant chemicals, especially in the US market, while market penetration is broadened by their use as alternative compounds to complement standard halogenated products. Further development of halogen/phosphorus synergism could lead to wider use as a substitute for antimony oxide. High value-added, halogen-free phosphorus compounds are expected to boost sales in volume and value. 

Similarly, reduction of both aromatic and aliphatic aldehydes and ketones where there is a chlorine (Cl) or bromine (Br) present elsewhere in the carbonyl-containing compound succeeds with sodium borohydride (NaBH,) and, occasionally, with lithium aluminum hydride (LiAIH,) at low temperatures. Catalytic reduction frequently leads to hydrogenolysis of the halogen, producing the halogen-free alcohol. 

In halogen-free PO systems, the zinc borate is recommended to be used in conjunction with ATH and/or Mg(OH)2 to achieve the most cost effective fire test performances. At a total loading of 80 150 phr, the weight ratio of ZB to ATH is normally in the range of 1 10 to 1 1. This combination can not only provide smoke reduction but can also form a porous ceramic residue, that is important thermal insulator for unburned polymer. The benefit of using the ZB and red phosphorous in halogen free PE insulator is illustrated in Table 4. 

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