Thiocyanation of phenols

Solvents that have been used with thiocyanogen include benzene, bromobenzene, carbon tetrachloride, chloroform, ether, ethylene bromide, carbon disulfide, petroleum ether, methyl acetate, nitromethane, and anhydrous formic and acetic acids. At low temperatures such solvents as saturated solutions of alkali thiocyanates in methanol or acetone can be used. The yield in the thiocyanation of amines is 20-30% higher when the reaction is carried out in a neutral medium like methanol rather than in acetic acid. The formation of a thiazole is also inhibited in a neutral solvent. Ether is usually not satisfactory because the solvent is attacked and because some of the amine is precipitated as the thiocyanate. On the other hand, thiocyanation of phenols appears to give better yields in acetic acid solution than in neutral solvents. 

Crompton [21] has reviewed the use of electrochemical methods in the determination of phenolic and amine antioxidants, organic peroxides, organotin heat stabilisers, metallic stearates and some inorganic anions (such as bromide, iodide and thiocyanate) in the 1950s/1960s (Table 8.75). The electrochemical detector is generally operated in tandem with a universal, nonselective detector, so that a more general sample analysis can be obtained than is possible with the electrochemical detector alone. 

Thiocarbonates, synthesis of, 17, 3 Thiocyanation of aromatic amines, phenols, and polynuclear hydrocarbons, 3, 6 Thiophenes, synthesis of, 6, 9 Thorpe-Ziegler condensation, 15, 1 31 Tiemann reaction, 3, 9 Tiffeneau-Demjanov reaction, 11, 2 Tin(n) enolates, 46, 1 Tin hydride method to prepare radicals,... 

St.Louis, MO), and RNA STAT-60 (TEL-TEST B, Inc, Friendswood, TX), or similar ready-to-use RNA extraction reagents. It is also possible to isolate RNA, DNA, and proteins simultaneously from the tissue homogenate using guanidine-thiocyanate and phenol [20,21], Since DNA is trapped in the interphase and the phenol phase under acidic pH during extraction, the addition of an equal volume of 1 M Tris solution (pH 10.5) to the phenol phase raises the pH and thereby increases the solubility of the DNA in the aqueous phase. This DNA can be recovered by ethanol precipitation. 

A variety of phenols and naphthols were converted efficiently into 4-thiocyanato derivatives by (dichloroiodo) benzene and lead thiocyanate. 

To an ice-cooled suspension of lead thiocyanate (485 mg, 1.5 mmol) in dry dichloromethane (10 ml) was added (dichloroiodo)benzene (330 mg, 1.2 mmol). The mixture was stirred for 20 min at 0°C and then the phenol (1 mmol) was added and the whole mixture was stirred for 1 h. The reaction mixture was filtered and silica (2 g) was added to the filtrate, which was concentrated. The product was adsorbed on silica and eluted with ethyl acetate-hexane to give the 4-thiocyanated phenol (61-95%) or naphthol (58-97%). In no case was any 2-isomer found. An alternative, more expensive, procedure for the thiocyanation of aromatics involved BTI (Section 4.5). 

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]. 

The current response of a GCE used for AMD was greatly improved after modification with polyhistidine. LOD was 6 nM for dopamine (10a), 8 nM for epinephrine (15a) and 20 nM for catechol (42). The modified electrode has also been applied for AMD after CE37. PVC membranes were designed to serve as selective barriers for the amperometric detection of phenols and elimination of thiocyanate interference . 

A combination of PhICl2 and Pb(SCN)2 is an effective reagent for thiocyanation of silyl enol ethers [80a], alkynes [80b], and phenols [80c] (Scheme 13.61). Such reactions are thought to proceed via in-situ generation of PhI(SCN)2. It has been reported fhat the presence of the weak Lewis acid PbCl2 generated in situ seems to accelerate fhe reaction with phenol. 

Cyanogen chloride reacts with sodium sulfide, Na2S, to form sodium thiocyanate, NaSCN. An extension of this involves the reaction of thiolate anions, RS, with CICN to form thiocyanates, RSCN. Similarly, the reaction of phenols produces aromatic cyanates (Kaupp et al., 1998). In such reactions, 3° amines are used to trap hydrogen chloride. 

The procedure given above is a convenient method involving the formation of an active thiocyanogen derivative in the presence of dimethylaniline. Thiocyanation of aromatic amines and phenols has also been accomplished electrochemically. ... 

An improved method for the thiocyanation of 2-arylindan-l,3-diones, phenols and anilines employs a reagent combination of (dichloroiodo)benzene and potassium thiocyanate in dry dichloromethane [596]. For example, the /tara-unsubstituted phenols and anilines 536 are efficiently converted under these reaction conditions into the respective /7-thiocyanato derivatives 537 in high yields (Scheme 3.210). 

The antioxidant activity of phenols used and standards was determined according to die ferric thiocyanate method with minor modifications. Each sample of treated wool (200 mg) was mixed with 2 mL distiUed water and 5 mL linoleic acid emulsion (0.02 M, pH 7.0) and 5 mL phosphate bufier (0.2 M, pH 7.0). Linoleic acid emulsion was prepared by mixing 0.5608 g of linoleic acid with 0.5608 g of Tween 20 as emulsifier, and 100 mL phosphate buffer (0.2 M, pH 7.0), and then the mixture was homogenised. The reaction mixture was incubated at 37 C. Aliquots of 0.1 mL wm taken at different intervals during incubation. The degree of oxidation was measured by sequentiaUy adding 4.7 mL ethanol (75%), 0.1 mL ammonium diiocyanate (30 %), 0.1 mL sample solution and 0.1 mL ferrous chloride (0.02 mg, in 3.5% HCl). The mixture was... 

Several new methods have been put forward for the functionalization of benzene derivatives. 1. S. Yadav of the Indian Institute of Chemical Technology, Hyderabad has devised (Chem. Lett. 2008, 37, 652) a procedure for direct thiocyanation, converting 1 into 2. Sukbok Chang of KAIST has established Chem. Commun. 2008, 3052) that both NH Cl and aqueous NHj could be used to directly aminate an aryl iodide such as 3. lohn F. Hartwig of the University of Illinois has developed J. Am. Chem. Soc. 2008,130, 7534) a protocol for the directed borylation of anilines such as 5 and of phenols, based on a transient sUyla-tion. Karsten Menzel of Merck West Point Tetrahedron Lett. 2008, 49,415) has observed selective exchange of tribromobenzene derivatives such as 7, with the direction of the selectivity being controlled by the fourth substituent on the benzene. 

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