Phosphorus dibromide

Treating 113 (easily available from 45 by reaction of its dilithio derivative with formaldehyde and treatment of the resulting diol with phosphorus dibromide) with the so-called Mori reagent [72], a trimethylsilyl(tri-n-butyl)stannane/cesium fluoride combination that has been used very successfully in many debromination reactions [73], results in the production of the [6.6]paracyclophane 115 in acceptable yield. Since p-xylylene (p-quinodimethane) is known to dimerize to [2.2]paracyclophane, it may well be that the bis(cumulene) 114 is formed as an intermediate in this reaction. Since a stepwise process is also conceivable, further clarification of the mechanism is obviously desirable (Scheme 25). 

Dibromobutane (from 1 4-butanediol). Use 45 g. of redistilled 1 4-butanediol, 6-84 g. of purified red phosphorus and 80 g. (26 ml.) of bromine. Heat the glycol - phosphorus mixture to 100-150° and add the bromine slowly use the apparatus of Fig. Ill, 37, 1. Continue heating at 100-150° for 1 hour after all the bromine has been introduced. Allow to cool, dilute with water, add 100 ml. of ether, and remove the excess of red phosphorus by filtration. Separate the ethereal solution of the dibromide, wash it successively with 10 per cent, sodium thiosulphate solution and water, then dry over anhydrous potassium carbonate. Remove the ether on a water bath and distil the residue under diminished pressure. Collect the 1 4-dibromobutane at 83-84°/12 mm. the yield 3 73 g. 

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Whereas l,2-0-isopropylidene-5,6-di-0-methyl-D-glucofuranose was found to be unreactive towards triphenylphosphite dibromide, triphenylphosphite methiodide or phosphorus pentachloride, the related methyl 2,5,6-tri-0-methyl-/ -D-glucofuranoside (59), in which the hindrance caused by the ketal group is absent, reacted with triphenylphosphite methiodide to give the 3-deoxy-3-iodo derivative 60 in 31% yield. 

A solution of 52.8 g. (0.20 mole) of o-xylylene dibromide (Note 6) in 300 ml. of purified dimethylformamide is added dropwise with stirring at such a rate as to maintain a temperature of 60-70° (Note 7). Subsequently the reaction mixture is stirred at room temperature for 3 hours and then poured into 600 ml. of ice water in a 2-1. Erlenmeyer flask. After standing at room temperature overnight the product is collected by suction filtration, pressed on the funnel, and washed twice with 100-ml. portions of water. The crude product is air-dried on filter paper for 2-3 hours and is then dissolved in 1.21. of boiling 95% ethanol. The solution is filtered through a heated funnel, and the filtrate is refrigerated overnight. The crystals are collected on a Buchner funnel and washed on the funnel with 100 ml. of cold 95% ethanol. The product is dried over phosphorus pentoxide in a vacuum desiccator. The yield of white crystals of 2-(% tolylsulf onyl)-dihydroisoindole is 41-46 g. (75-84%), m.p. 174-175° (dec.). 

Diselenium dichloride and seleninyl chloride both explode on addition of potassium [1,3], while the metal ignites in contact with phosphorus trichloride vapour or liquid [2], Mixtures of potassium with sulfur dichloride or sulfur dibromide, phosphorus tribromide or phosphorus trichloride, and with phosgene are shock-sensitive, usually exploding violently on impact. Potassium also explodes violently on heating with disulfur dichloride, and with sulfur dichloride or seleninyl bromide without heating [3]. 

Either the white or red form incandesces with boron triiodide [1]. Red phosphorus incandesces in seleninyl choride while white explodes. Red phosphorus reacts vigorously on warming with sulfuryl chloride or disulfuryl chloride, and violently with disulfur dibromide [2],... 

An attempt to prepare 1 -bromo-2-fluoroethane by the partial fluorination of ethylene dibromide by means of antimony trifluoride was not very successful. The compound was best prepared by the action of phosphorus tribromide on F.E.A. The compound was relatively non-toxic and the bromine atom rather unreactive, but considerably more reactive than the chlorine atom in chlorofluoroethane. For example, bromofluoroethane was readily converted by means of potassium thiocyanate into 2-fluoroethyl thiocyanate. As a lethal inhalant the toxicity of the thiocyanate was inferior to that of M.F.A. Toxicity by injection, however, appeared to be higher. 

Several papers have been devoted to the subject of reactions of phosphoranes with carboxylic acids and their derivatives. Thus triphenylphosphine dibromide (111) in acetonitrile cleaves lactones,93 while the corresponding dichloride (112) converts esters into acid chlorides.94 The reactions of esters with phosphorus pentachloride (101) have been studied further,95 and the influence of structural changes on the yields of products (113) and (114) has resulted in minor modifications to the mechanism previously96 outlined. 

The starting diol was transformed into the dibromide by elemental bromine with triphenyl phosphine adduct which undergoes the Arbuzov-Michaelis reaction under somewhat drastic conditions at 150 °C (step a). Catalytic removal of the benzyl group was performed by a Pd/C catalyst (step b) and the alcohol formed was allowed to react with dichloropurine in the presence of triphenylphosphine and diethylazodicarboxylate (Mit-sunobu reaction) (step c). Finally the desired product was obtained by reaction with methylamine (step d) and the removal of ethyl groups at the phosphorus centre was performed by transilylation using trimethyliodosilane (step e). 

Treating phosphorus trifluoride with bromine and then heating the product phosphorus trifluoride dibromide, PFsBr2 ... 

Halogenation of dibenzofuran produces the 2-halo compounds. Bromina-tion can be achieved in good yield with bromine in acetic acid " or with N-bromosuccinimide in boiling carbon tetrachloride. The 2,8-dibromo compound has been made, using dioxane dibromide. Chlorination of dibenzofuran in acetic acid in the presence of iron powder can be controlled to yield the 2-chloro or the 2,8-dichloro compounds. 2-Chlorodi-benzofuran is best prepared by reaction of dibenzofuran with phosphorus pentachloride. 2-Iododibenzofuran (45%) results from treatment of dibenzofuran with iodine in boiling chloroform in the presence of nitric acid. 2,8-Diododibenzofuran is best prepared by reaction of dibenzofuran with iodine and iodic acid in aqueous acetic acid. ... 

G. W. F. Holroyd to be a conductor, and the introduction of phosphorus trichloride, and of hydrogen chloride reduced the conductivity a soln. of the pentachloride in ethylene dibromide, benzene, or phosphorus trichloride passed no current. 

The reaction of alkenyl alkyl ethers and ketene acetals with PX3 (X = Cl or Br) has been reported to occur readily in the presence of an organic base and to result in the electrophilic substitution of a vinyl hydrogen atom with the PX2 group. Thus, (2-alkoxyalkenyl)-, (l-bromo-2-alkoxyalkenyl)- and (2,2-dialkoxyalkenyl)-phosphorus dichlorides and dibromides were obtained in 70-98% yield. The reaction proceeds regio- and stereo-selectively and is believed to involve formation of a cyclic phosphirenium ion.74... 

Nonmetal Halides. Vigorous or explosive reactions occur with phosphorus tribromide on addition of drops of water,20 phosphorus trichloride, phosphorus pentachloride,21 diselenium dichloride,22 sulfur dichloride, boron tribromide, sulfur dibromide,17 seleninyl bromide,23 phosphoryl chloride, sulfinyl fluoride, silicon tetrachloride, and silicon tetrafluoride.24... 

---