Thiuronium salt

Note. The treatment of amides with. nitrous add, to obtain the free acid more rapidly than by alkaline hydrolysis, is in general inadvisable when preparing the thiuronium salts.)... 

S-Alkyl-iso-thiuronium picrates. Alkyl bromides or iodides react with thiourea in alcoholic solution to produce S-alkyl-iso-thiuronium salts, which yield picrates of sharp melting point ... 

S-Benzyl-[Pg.363]

S-Benzyl-wo-thiuronium chloride (S-benzyl-iao-thiourea hydrochloride) reacts with the alkali metal salts of organic acids to produce crystalline S benzyl-MO-thiuronium salts ... 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

The excess of alkah is then neutralised with dilute hydrochloric acid (phenolphthalein) and the solution is evaporated to dryness on the water bath. The acid may then be characterised as the S-benzyl-tao-thiuronium salt or as the p-bromophenacyl ester (Section 111,85). In many instances the derivative may be prepared directly from the neutralised solution. 

Also known as S-benzylthiuronium salts and as S-benzyl- -thiuronium salts. 

The amine is removed by the addition of alkali and characterised by a suitable derivative the sulphonic acid may then be recovered as the sodium salt and converted into a crystalline derivative, e.g., the S-benzyl-tso-thiuronium salt. 

Saponification of esters. Aqueous sodium hydroxide method. To hydrolyse an ester of an alcohol, reflux 5-6 g. with 50 ml. of 20 per cent, sodium hydroxide solution for 1-2 hours or until the ester layer disappears. Distil the alkahne mixture and collect about 6 ml. of distillate. This will contain any volatile alcohol formed in the saponification. If the alcohol does not separate, i.e., is water-soluble, saturate the distillate with sohd potassium carbonate an upper layer of alcohol is then usually formed. (The alcohol may be subsequently identified as the 3 5-dinitrobenzoate see Section 111,27,2.) Cool the residual alkahne mixture, and acidify it with dilute sulphuric acid. If no crystalline acid is precipitated, the acid may frequently be isolated by ether extraction, or it may be distilled from the acidified solution and isolated from (or investigated in) the distfllate. (The acid may be subsequently identified, e.g., as the S benzyl wo-thiuronium salt see Section 111,85,2.)... 

Sulphonic acids. The aromatic sulphonic acids and their alkali metal salts are soluble in water, but insoluble in ether (Solubility Group II). They are best characterised by conversion into crystalline S-benzyl-iso-thiuronium salts (see Section IV,33,2 and 111,85,5), which possess characteristic melting points. A more time-consuming procedure is to treat the well-dried acid or... 

Also known as S-benzylthiurouium salts and as S-benzyI-0-thiuronium Salts. 

Now distil the filtrate A) and collect the distillate as long as it is acid to litmus. Should any solid separate out in the distilhng flask during the distillation, add more water to dissolve it. Set aside the residue (B) in the flask. Identify the volatile acid in the distillate. A simple method is to just neutralise it with sodium hydroxide solution, evaporate to dryness and convert the residual sodium salt into the S-benzyl-wo-thiuronium salt (Section 111,85,5). 

Thiourea derivatives 169 are also suitable starting materials for the preparation of pyrido[ l,2-r/][ l,3,4]oxadiazincs. Thus, reacting 169 with methyl iodide to yield the corresponding thiuronium salt, its treatment with base gave the cyclized products 155 or 170 (Scheme 20) <1997H(45)927>. 

Even when allyl iso-thiuronium salt (and NaOH) is used tractably as a precursor of thiol (DMF, 40°C), the extent of thioetherification is nearly equal to that for the case 1). 

Thioetherification of PECH is feasibly performed in DA-solvents as already described in the patent (20J. For example, the highest substitution was obtained by the reaction of P(ECH-EO)(1 1 copolymer of epichloro-hydrin and ethylene oxide) and equimolar thiophenoxide in HMPA at 100°C for 10 h as DS 83% for sodium and 93% for potassium salts. The DS in our nucleophilic substitution was estimated by the elemental analysis as well as the titration of liberated chloride ion with mercuric nitrate (21). In the latter method, reacted medium was pretreated with hydrogen peroxide when the reductive nucleophiles which can react with mercuric ion were used. As described before for PVC, thiolation was also achieved conveniently with iso-thiuronium salt followed by alkaline hydrolysis without the direct use of ill-smelling thiolate. The thiolated PECH obtained are rubbery solids, soluble in toluene, methylene chloride, ethyl methyl ketone and DMF and insoluble in water, acetone, dioxane and methanol. 

In the cyclization of the tram isomers 121 ( = 1, 2 R = H, Me), no difference was found in the reactions. The cyclizations proceeded in good yields (72-84%), resulting in 122 in all four cases (n = 1, 2 R = H, Me) (85T5981). The cyclizations to 1,3-oxazines took place with retention, which is in agreement with the suggested mechanism formation of the thiuronium salt and subsequent nucleophilic attack of the oxygen on the partially positive carbon. 

Most of the now synthetically used quantitative cascade reactions involve an initial substitution step. That is quite clear for the reactions of acyl hahdes with thioureas to give 2-aminothiazoliiun salts. The 3-cascade consists of substitution to form the thiuronium salt, specific cychzation with the more nucleophihc of the amino groups, and elimination of water. In all reported cases, the water of reaction is taken up by the product crystal and it can be removed by heating to about 80 °C in a vacuiun. For example, if the thioureas 162 and phenacyl bromide 217 are stoichiometrically ball-milled at room temperature for 30 min, quantitative yields of the pure products 428 are obtained in all cases after drying at 0.01 bar at 80 °C [ 10] (Scheme 67). The free bases 429 can be obtained by trituration of 428 with NaHCOj solution. Furthermore, the thioureido-acet-amides 275 react correspondingly with 217 to give quantitative yields of the salts 430 from which the free bases can be obtained by NaHCOj trituration [96]. 

S Benzy liso thiuronium salts (S-Benzylisothiourea salts). 

Keywords mercaptobenzothiazole, chloroacetone, gas-solid reaction, thiuronium salt... 

A one-step allylic rearrangement-of a 17/3-hydroxy-17a-vinyl steroid (21) in acidified acetic acid-acetic anhydride gave the 21-acetoxypregn-17(20)-ene (22) in 60—65% yield,59 improving upon an earlier two-step sequence via the 21-chloro-derivative. 17/8-Hydroxy-17a-vinyl steroids (21) are converted into ( )-pregn-17(20)-enes (24) by reaction first with thiourea and hydrochloric acid to give the rearranged thiuronium salt (23), followed by reduction with sodium-ammonia.60... 

Cyclizations by formation of carbon-sulfur-bonds belong to the best studied reactions which use the dilution principle. Usually bromides react with thiols [7 b, 17, 18], thiuronium salts [19], or with sodium sulfide [20] and thioacetamide, respectively. The formation of C—S bonds represents one of the most valuable methods to synthesire medium-membered cyclophanes such as 4-8 [7 b, 18 b, 20d, 21]. 

Thiourea is known to behave as a C nucleophile at its sulfur atom toward an alkylating cigent to yield thiuronium salt. From the similarity in the resonance structures between thiourea and diaminocyclopropenethione (79). as shown in Fig. 5, it might be expected that diaminocyclopropenethione when allowed to react with an alkylating agent (electrophile) wiU afford the diaminoalkylthiocyclopropenium ion (37). 

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