Isothiocyanate bonding

The isothiocyanate of the monoanilino porphyrin (Scheme 6.8.1) binds covalently in the form of single molecules to gold(lll). The porphyrin molecules lie flat on the surface. STM revealed preferential localizations on this surface leading to an appearence of string of pearls. The isothiocyanate bond to gold is heat and oxidation resistant (Tao et al., 1995). 

Hydroxy-THISs add regioselectively to the C=N bonds of isocyanates and isothiocyanates producing stable adducts (Scheme ID (19). 

Hydroxy-THISs add regioselectively to the C=N bonds of isocyanates or isothiocyanates. The initially formed cycloadducts eliminate carbonyl sulfide with formation of 4-hydroxy- or 4-mercaptoimidazolium hydroxide inner salts (21) (Scheme 21). 4-Hydroxyimidazolium hydroxide... 

Chemical Properties The formation of salts with acids is the most characteristic reaction of amines. Since the amines are soluble in organic solvents and the salts are usually not soluble, acidic products can be conveniendy separated by the reaction with an amine, the unshared electron pair on the amine nitrogen acting as proton acceptor. Amines are good nucleophiles reactions of amines at the nitrogen atom have as a first step the formation of a bond with the unshared electron pair of nitrogen, eg, reactions with acid anhydrides, haUdes, and esters, with carbon dioxide or carbon disulfide, and with isocyanic or isothiocyanic acid derivatives. 

Azoles containing a free NH group react comparatively readily with acyl halides. N-Acyl-pyrazoles, -imidazoles, etc. can be prepared by reaction sequences of either type (66) -> (67) or type (70)->(71) or (72). Such reactions have been carried out with benzoyl halides, sulfonyl halides, isocyanates, isothiocyanates and chloroformates. Reactions occur under Schotten-Baumann conditions or in inert solvents. When two isomeric products could result, only the thermodynamically stable one is usually obtained because the acylation reactions are reversible and the products interconvert readily. Thus benzotriazole forms 1-acyl derivatives (99) which preserve the Kekule resonance of the benzene ring and are therefore more stable than the isomeric 2-acyl derivatives. Acylation of pyrazoles also usually gives the more stable isomer as the sole product (66AHCi6)347). The imidazole-catalyzed hydrolysis of esters can be classified as an electrophilic attack on the multiply bonded imidazole nitrogen. 

Other functional groups that are easily differentiated are cyanide (5c =110-120) from isocyanide (5c = 135- 150), thiocyanate (5c =110-120) from isothiocyanate (5c = 125 - 140), cyanate (5c = 105- 120) from isocyanate (5c = 120- 135) and aliphatic C atoms which are bonded to different heteroatoms or substituents (Table 2.2). Thus ether-methoxy generally appears between 5c = 55 and 62, ester-methoxy at 5c = 52 N-methyl generally lies between 5c = 30 and 45 and. S-methyl at about 5c = 25. However, methyl signals at 5c = 20 may also arise from methyl groups attached to C=X or C=C double bonds, e.g. as in acetyl, C//j-CO-. 

A major advance was devised by Pehr Edrnan (University of Lund, Sweden) that has become the standard method for N-terminal residue analysis. The Edman degradation is based on the chemistry shown in Figure 27.12. A peptide reacts with phenyl isothiocyanate to give a phenylthiocarbamoyl (PTC) derivative, as shown in the first step. This PTC derivative is then treated with an acid in an anhydrous medium (Edrnan used nitrornethane saturated with hydrogen chloride) to cleave the amide bond between the N-terminal anino acid and the remainder of the peptide. No other peptide bonds are cleaved in this step as amide bond hydrolysis requires water. When the PTC derivative is treated with acid in an anhydrous medium, the sulfur atom of the C=S unit acts as... 

The reaction of the morpholine enamine of cyclohexanone with phenyl isothiocyanate led only to the tetrasubstituted isomer of the monoadduct (54), which failed to add any more of the phenyl isothiocyanate. The formation of only the tetrasubstituted isomer has been attributed by Hunig et al. (37) to the stronger conjugation of the C=S group with the enamine double bond than that of the C=0 group in the enamine (49). 

It is worth noting that the 2-pyridone 42 (99MI1) and thione 43 (88H(27)733), which could react in either of the two ways as shown, with an isocyanate or isothiocyanate and with a nitrile respectively, actually give a one-carbon insertion. There is a case of formation of 2,3 and 3,4 bonds in the preparation of 8-hydroxy-triazolopyridine 44 (83MI1). 

Related to this process is the hydrolysis of isocyanates or isothiocyanates" where addition of water to the carbon-nitrogen double bond would give an N-substituted carbamic acid (3). Such compounds are unstable and break down to carbon dioxide (or COS in the case of isothiocyanates) and the amine ... 

Note that carbon monoxide inserts into the Zr-H bond of 1 (2 equiv.) to afford an T -formaldehydo-type complex [(Cp2ZrCl)]2(g-CH20) [200-202]. Iminoacyl zir-conocene complexes are formed after addition of 1 to isonitriles [203]. Carbon dioxide [183, 202] is reduced to formaldehyde with 1 (2 equiv.). C02-like molecules such as isocyanates RNCO [204], isothiocyanates RNCS [205], and carbodiimides RNCNR [204] are readily converted to the corresponding bidentate form-amido ligands. 

As in the case of silanone 9, the reaction of the silylene bis[2-(dimethylamino-methyl) phenyl]silanediyl (8) with phenyl isothiocyanate was examined.29 In this reaction the expected silanethione 36 was obtained as a single product even in the presence of (Me2SiO)3, no insertion product of 36 into a Si-O bond of (Me2SiO)3 was observed (Scheme 10). 

Various isothiocyanates (RNCS R = Buc, Ph) and CS react with exclusively with the Mg-C bonds of dinuclear Al-Mg compounds to give dinuclear insertion products (Scheme 7). In the case of the reaction of Me2Al(/i-Et2N)2Mg(CH3) 2 with PhNCO, a tetranuclear insertion product is formed.290... 

Figure 9.52 The isothiocyanate group of a TMT europium chelate can be used to label amine-containing proteins and other molecules to result in an isothiourea bond.

Figure 10.2 The isothiocyanate group of DTTA can react with amine-containing molecules to form isothiourea bonds.

In this case, the acidic species RCOX is a hard acid and reacts with the nitrogen end of SCN to form an acyl isothiocyanate. The soft methyl group bonds to the S atom and forms methyl thiocyanate. Consider the reactions of NC)2 ... 

Thioureas are most commonly prepared from reaction of isothiocyanates with amines. Also there are some reports on reactions of anime or carbodiimides with several thionating reagents. AA -Disubstituted thioureas bearing double NH groups have been developed as sensors, and as catalysts because of their hydrogen bonding ability. A,A -Disubstituted thiourea-linked sugar chains have been prepared by the reaction of isothiocyanate with amine. 

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