Lead selenocyanates

Golub and Kosmatyi [59GOL/K.OS3], and Golub [59GOL] studied the complex formation between Pb and SeCN by potentiometric and solubility measurements. Both sets of experiments, carried out with the ligand in the concentration range of 0.7 to 3.6 M, 

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Lead Selenocyanate has been obtained as a lemon-yellow compound by the action of lead acetate on potassium selenocyanate. It is soluble in boiling water but is slightly decomposed. The salt may be exposed without decomposition to a temperature of 100° C., but when moist assumes a pink tint.1... 

GOL/KOS4] Golub, A. M., Kosmatyi, Y. V., A potentiometric study of lead selenocyanate, Russ. J. Inorg. Chem., 4, (1959), 606-608. From a citation in this Bibliography... 

A number of compounds of the types RBiY2 or R2BiY, where Y is an anionic group other than halogen, have been prepared by the reaction of a dihalo- or halobismuthine with a lithium, sodium, potassium, ammonium, silver, or lead alkoxide (120,121), amide (122,123), a2ide (124,125), carboxylate (121,126), cyanide (125,127), dithiocarbamate (128,129), mercaptide (130,131), nitrate (108), phenoxide (120), selenocyanate (125), silanolate (132), thiocyanate (125,127), or xanthate (133). Dialkyl- and diaryUialobismuthines can also be readily converted to secondary bismuthides by treatment with an alkali metal (50,105,134) ... 

Selenocyanic Acid, HCNSe, may be prepared in solution by decomposing the lead salt (obtained by treating potassium selenocyanate with lead acetate) with hydrogen sulphide.3 It is stable only in neutral or alkaline solution. Selenocyanuric acid has been obtained 4 as a red amorphous powder by the action of cyanuric chloride on sodium selenide and subsequent precipitation by acids. 

Heating the diselenoallene 140 leads to an intramolecular cycloaddition affording the fused selenin 141 (Scheme 15) <2001JOG1787>. The reaction appears to take place by an initial intramolecular hydrogen abstraction by the sp-hybridized carbon of the allene affording a diradical intermediate. Radical coupling then leads to the selenin. The cyclic allene precursor could be prepared by dilithiation of the benzylacetylene followed by treatment of the bis-selenocyanate. 

Various reducing agents have been used for the generation of selenolates from diselenides or selenocyanates. Alkali metals M (M = Li, Na, K)149,150 or alkali hydrides MH (M = Li, Na, K)151,152 can generate the corresponding selenolate anions such as 80 these are more reactive than the borane complexes of type 77 (Scheme 15). Diaryl diselenides are easier reduced than dialkyl diselenides, but the mechanism for the reduction of selenocyanates is complex and can lead to either diselenides or selenolates.153,154... 

Reactions leading to the formation of alkenic or a,/3-unsaturated bonds are very important in synthesis. This type of functionality is synthetically versatile, and of wide utility in the carbohydrate field. The use of sulfur reagents for conversion of sugar epoxides on vicinal disulfonates into al-kenes is well established97a 97b, and subsequent work with selenium reagents provided essentially comparable results. Thus, treatment of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside (219) with potassium selenocyanate in aqueous 2-methoxymethanol afforded methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-ery/firo-hex-2-enopyranoside (220).27 Similarly, treatment of 5,6-anhydro-l,2-0-isopropylidene-a-D-glucofuranose (221) with potassium selenocyanate in methanol at room temperature... 

Another useful system is o-nitrophenyl selenocyanate and tributylphos-phine (Bu3P), developed by Grieco and co-workers,104-106 which has been employed in the synthesis of intermediates leading to the ionophone antibiotic calcimycin.103... 

Phenols and aromatic amines are thiocyanated on electrolysis in an aqueous solution of SCN" [13]. The reaction is indirect since there is compelling evidence that the thiocyanat-ing reagent must be (SCN)2, formed by anodic oxidation of SCN"" [156]. In MeCN solution oxidation of SCN"" and SeCN in the presence of phenol of various aromatic amines leads to thiocyanation and selenocyanation in 55-80% yields 157 [109]. 

CDs could be used as leading electrolyte additives in isotachophoresis for improving the selectivity [58]. The addition of a-CD in the leading electrolyte contributed to the complete separation of compounds such as nitrite and nitrate ions, cyanate, thiocyanate and selenocyanate ions, chlorate and perchlorate ions. CDs were also successfully used as leading electrolyte additives in the capillary isotachophoretic separation of positional isomers, such as 2-, 3- and 4-amino phenols, 1,2-, 1,3- and 1,4-diaminobenenes, and substituted aromatic sulfonic acids. 

The formation of plumblte Ions HPb02 In strongly alkaline solutions has already been noted in section IV-4. This complex plays an Important role In some separation processes. A few other Inorganic complexes such as the selenocyanates, Pb(CNSe)2 and Pb(CNSe)g are known (G1)(G2) but have not been Important for lead analysis. 

A. M. Golub, "Study of the Selenocyanate Complexes of Lead. by the Solubility Method", Zhur. Neorg. Khlm.,4j 1577 ( 959)5 C.A. 8406 (i960)... 

Cyclic Disulphides and Cyclic Diselenides.—Formation. No fundamentally new methods of synthesis of this class of compounds have been reported in the past two years. For l,2>dithiolan the oxidation of l,3>dithiols remains a favoured method, the use of iodine in the presence of triethylamine leading smoothly to 1,2-dithiolans without attendant polymerization. cis- and tra/ -l,2-Dithiolan-3,5-dicarboxylic acids were prepared from a diastereo-isomeric mixture of dimethyl 2,4-dibromoglutarates by sequential treatment with potassium thioacetate and potassium hydroxide in the presence of iodine,and jyn-2,3-dithiabicyclo[3,2,l]octan-8-ol was formed from 2,6-dibromocyclohexanone by successive treatment with potassium thiocyanate, lithium aluminium hydride, and iodine. The stereoselective formation of the less thermodynamically stable alcohol in this case was attributed partly to the formation of chelates with sulphur-aluminium bonds. 2,2-Dimethyl-l,3-dibromopropane was converted into 4,4-dimethyl-l,2-diselenolan on treatment with potassium selenocyanate at 175 °C, but at 140 °C the product was 3,3-dimethylselenetan. Reductive debenzylation of 2-alkylamino-l,3-bis(benzylthio)propanes with lithium in liquid ammonia and oxidation of the resultant dithiols with air afforded 4-dialkylamino-l,2-dithiolans, whilst treatment of a-bromomethyl-chalcone with sodium hydrosulphide gave, as minor product, trans-3 phenyl-4-benzoyl-l,2-dithiolan. Among the many products of thermal decomposition of /ra/ -2,4-diphenylthietan was l,4,5,7-tetraphenyl-2,3-dithiabicyclo [2,2,2]octane. ... 

Sulfur, Selenium and Tellurium Derivatives. TMSCF3 reacts with elemental sulfur, selenium or tellurium in the presence of a fluoride anion, leading to trifluoromethylthiolates, seleniates or tellurates, respectively.Aryltrifluoromethyl-sulfides, sulfoxides and sulfones were obtained from the corresponding arylsulfenyl, sulfinyl and sulfonyl halides, respectively, by treatment with TMSCF3 and TASF. The reaction of disulfides and diselenides with TMSCF3 and TBAF gave trifluoromethyl thioethers and selenoethers, respectively (eq 26). The same procedure can also be carried out from thiocyanates and selenocyanates. 

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