Cobalt isothiocyanate

Cobalt isothiocyanate Diamorphine reacts to give a blue product on a pink background the other opiates do not react. Also reacts with tropane alkaloids and some benzodiazepines... 

This test allows greater discrimination. It is known that a number of products form blue complexes with the cobalt isothiocyanate, although these do not extract into the chloroform as readily, or if at all. 

This is a modification of the previous test, with the reagent consisting of a 2% (wl/vol) solution of cobalt isothiocyanate in water, diluted with an equal volume of glycerine (1), concentrated hydrochloric acid (2) and chloroform (3). Testing for cocaine is carried out as follows. A small amount of the material is placed in a test-tube and five drops of component (1) added, when a blue colour will develop if cocaine is present. One drop of concentrated hydrochloric acid (2) is then added and the blue colour, if this has resulted from the presence of cocaine, should disappear, leaving a pink solution. Further confirmation is provided by the addition of several drops of chloroform (3), whereupon an intense blue colour... 

What advantage does this modified test have over the cobalt isothiocyanate approach ... 

Chelated species are less common. The substituted thiourea 7V-ethoxycarbonyl-/V-[3-(/>-anisyl) pyrazol-5-yl]thiourea (eatu) acts as a monoanionic 0,S-chelate to cobalt(II), forming Co(eatu)2.506 Whereas ethylenethiourea (etu) has been observed to act as a S-donor monodentate in Co (etu)2X2(H20)2 (X = C1, Br), it binds as an S,N-chelate in Co(etu)2(OOCCH3)2.507 Both violet octahedral and blue tetrahedral cobalt(II) compounds Co(pptu)2Cl2 and Cp(pptu)Cl2 respectively were prepared with bidentate A -2-(5-pico 1 y 1)- A"-pheny 11hiourea (pptu) chelated.508 Refluxing Co powder with thiourea in 4-methylpyridine provides a route to isothiocyanates, which form by decomposition of thiourea to ammonium thiocyanate509 with one product, Co(pic)4(NCS)2, characterized by a crystal structure. 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

Among the other notations is that acetaldehyde is to be avoided, it being a respiration inhibitor. It is related to ethyl alcohol or ethanol and also to acetic acid, but not necessarily to citric acid as involved in the carboxylic acid or citric acid cycle. Alkaloids are expectedly respiration inhibitors, and anesthetics can have respiration inhibition as a side effect. Aromatic adds such as phenol are bad news, as are arsenate, cyanide, isothiocyanate, and thiocyanate. The heavy metals cadmium, cobalt, copper, ruthenium, vanadate, and zinc are regarded as health risks, if not for respiration, for other reasons. 

Table 8 shows cobalt complexes derived from organic isothiocyanates. 

Catalysed aerobic epoxidation of the styrene-cobalt complex, followed by the addition of trimethylsilyl isothiocyanate, yields 4-phenyloxazolidine-2-thione 123 <96TL7315>. The 4-substituted 2-oxazolidinone 124 undergoes a "chromium Reformatsky" reaction with aldehydes RCHO (R = i-Pr or Ph) in the presence of chromium(ll) chloride and lithium iodide to give mainly the unusual anti-aldol products 125 in excellent dia,stereomeric excess and yield <97TL4,387>. 

Cyclopentadienylbis(triphenylphosphine)cobalt catalyzes the oligomerization of acetylenes and cooligomerization of acetylenes and nitriles or acetylenes and isothiocyanates, RNCS " [scheme (9.165)]. 

The liganded cobalt isonitfile complexes 75 react with isothiocyanates to give the rearranged [2-1-2] cycloadducts 76 . 

Cobalt-catalysed cyclotrimerization of alkynes R C=CR with isocyanates R NCO and the carbodi-imide PhN=C=NPh constitutes a new synthesis of the 2-0X0- and 2-imino-l,2-dihydropyridines (20 X = O) and (20 X = NPh) respectively. Attempts to extend the process to the preparation of pyridine-2-thiones by using an isothiocyanate-alkyne mixture failed in that preferential desulphurization of the isothiocyanate took place. Chloro-cyanines, e.g. (21), prepared... 

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