Sodium iodide phosgene

Methyl 4,6-0-benzylidene-3-deoxy-a-D-ribo-hexopyranoside (56) was benzoylated, debenzylidenated, and partially p-toluenesulfon-ylated to 57 this was converted into 58 by reaction with sodium iodide, followed by catalytic reduction. The methanesulfonate of 58 was converted into 59 by reaction with sodium azide in N,N-dimethylformamide, and 59 was converted into 4-azido-3,4,6-trideoxy-a-D-xylo-hexose (60) by acetolysis followed by alkaline hydrolysis. Reduction of 60 with borohydride in methanol afforded 61, which was converted into 62 by successive condensation with acetone, meth-anesulfonylation, and azide exchange. The 4,5-diazido-3,4,5,6-tetra-deoxy-l,2-0-isopropylidene-L-ara/uno-hexitol (62) was reduced with hydrogen in the presence of Raney nickel, the resultant diamine was treated with phosgene in the presence of sodium carbonate, and the product was hydrolyzed under acidic conditions to give 63. The overall yield of 63 from 56 was 4%. The next three reactions (with sodium periodate, the Wittig reaction, and catalytic reduction) were performed without characterization of the intermediate products, and gave (+)-dethiobiotin methyl ester indistinguishable from an authentic sample thereof prepared from (+)-biotin methyl ester. 

In the absence of water, phosgene reacts quantitatively with sodium iodide in acetone solution according to the equation COCI2 2NaI = CO I2 -j- 2NaCl. 

The Sodium Iodide Method. The determination of phosgene by this method, due to the Chemisch-Technischen Reichsanstalt, is carried out by titrating the iodine liberated when a gas mixture containing phosgene but free from acid gases, reacts with a solution of sodium iodide in acetone. The reaction is as follows ... 

As the reaction between sodium iodide and phosgene proceeds quantitatively only in absence of water, the sodium iodide should be dissolved in acetone which has been dried for several days over calcium chloride. 

If Kdlliker s apparatus is used to determine phosgene in presence of hydrochloric acid, zinc dust cannot be used as it has too great a resistance. In this case the gas mixture to be tested is first passed through a wash bottle containing a sulphuric acid solution of silver sulphate (3 gm. in 100 ml. sulphuric acid of S.G. 1 84) and then through the acetone solution of sodium iodide. 

At the end of the operation, 5 ml. of ammonia are added to the alkaline solution and i ml. 10% sodium iodide solution, after which the hydrocyanic acid present is titrated with N/20 silver nitrate solution. The number of ml. of silver nitrate employed, multiplied by o 00365 gives the amount of hydrochloric acid present in the sample of phosgene employed. 

Monochloromethyl chloroformate, like phosgene, liberates iodine from sodium iodide, but the reaction is not quantitative, proceeding only to about 70% completion. ... 

A military specification [1394a] suggests the determination of phosgene by reaction of phosgene with a solution of sodium iodide in propanone, and titration of the liberated iodine with sodium thiosulfate (see Section 3.2.1.2), correcting for any free chlorine present. 

When phosgene has been determined with sodium iodide in propanone (Section 4.6.1), acid content may be determined by titrating (phenolphthalein indicator) the resultant solution with standard aqueous sodium hydroxide solution [1394a]. 

Similarly, the reactions between solid sodium iodide and either phosgene or carbonyl dibromide at -78 C produced only CO, Ij and NaX (X = Cl or Br) [1589b], and a reaction between tetrabutylammonium iodide and phosgene in dichloromethane at -78 C yielded only CO, Ij and [NBu ]Cl [1589b]. These results, particularly those obtained at low temperature, clearly point to COIj, even if it was formed as a transient intermediate, being extremely unstable. 

Titration phosgene and triphosgene liberate iodine from sodium iodide in acetone. 

The sodium salts of dialkyl l-(alkoxycarbonyl)methylphosphonates. in the presence of a further equivalent of NaH, undergo addition of carbon disulfide in EtjO at room temperature to give alkenedithiolates, which are characterized by protonation, alkylation (Mel, EtI, BnCl), oxidation, and phosgenation. For example, reaction with metliyl iodide provides the dialkyl 1-alkoxycarbonyl-2,2-/7i.v(mcthylthio)vinylphosphonates in good yields (68-75%), whereas room-temperature treatment with acetyl or benzoyl clilonde produces l,3-dithietane-2,4-diylidene-foZ5 [(alkoxycarbo-nyl)methylphosphonates] in moderate yields (18-39%, Scheme 8.23). The same oxidation product is obtained by reaction with iodine. 

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