Compounds containing the PNCO grouping can be obtained e.g. from phosphorus halides and silver cyanate or esters of N-chloroiminocarbonic acid and by thermal decomposition of alkoxycarbonylimino-phosphoranes. The phosphorus( vj isocyanates resemble the "carbon" isocyanates in their chemical properties, whereas the phosphorus(rrrj isocyanates resemble the phosphorus(mj chlorides. Some of the compounds discussed have insecticidal or cytostatic actions.
We recently ascertaincd that amidines (1) resct very readily with oxalyl dichloride to give imidazoline-4,5-dione hydrochlorides (2) [ 1~2 1 .
Vor kurzem berichteten wir "1 uber eine einfache Methode zur Synthese von Phosphor-und Thiophosphorsaure-diesterisocyanaten (2) durch Einwirkung von Oxalsauredichlorid auf entsprechende Phosphorsaure-diester-amide (I). Die Reaktion fuhrt man in inerten Losungsrnitteln (2.B. CC14, Benzol) bei 0 "C durch.
Verbindungen mil der PNCO-Gruppierung sind z. B. aus Phosphorhalogeniden und Silbercyanat oder N-Chloriminokohlensaureestern sowie durch thermische Zersetzung von Alkoxycarbonyliminophosphoranen zu erhalten. In ihren chemischen Eigenschaften rihneln die Phosphor(v)-isocyanate den ,,Kohlenstof'-isocyanaten, die Phosphor(xn)isocyanate dagegen den Phosphor(xi1)-chloriden. Einige der besprochenen Verbindungen haben insektizide oder cytostatische Wirkung.Aryl-, Alkyl-und Acylisocyanate sind seit uber hundert Jahren bekannt und sehr gut untersucht. Verbindungen, deren NCO-Gruppen nicht an Kohlenstoff, sondern an ein anderes Element (P, As, Si, Sn, B usw.) gebunden sind, konnten dagegen erst vor kurzem dargestellt werden. Die ersten Phosphorisocyanate wurden zwar schon 1940 erhalten; bis 1954 war die Stoffklasse aber schwer zuganglich und kaum untersucht. Die intensive Entwicklung dieses Gebietes begann erst, als einfachere und bequemere Methoden zur Gewinnung der Verbindungen gefunden waren.Phosphorisocyanate werden u. a. fur die Herstellung phosphorylierter Urethane und Harnstoffe benutzt. Unter den Phosphorisocyanaten sind physiologisch sehr aktive Substanzen. Einige von ihnen haben praktische Verwendung als Insektizide und Arzneimittel gefunden (s. Abschnitt 4.). Gegenwartig sind folgendeTypen bekannt: Phosphor(rrr)-isocyanate: XzPNCO und XP(NC0)z rnit X -Hal, Alkoxy, Aryloxy, Alkyl und Aryl; auDerdem P(NCO)3 und Pz(NCO)4. Phosphor(v)-isocyanate: XlXzP(0)NCO mit XI = X2 -Hal, Alkyl, Aryl, Alkoxy, Aryloxy. Dialkylamino, Diarylamino; XI -Hal, Xz = Alkoxy, Aryloxy, Alkyl oder Aryl; XI -Alkyl oder Aryl, Xz = Alkoxy, Aryloxy, Dialkylamino, Diarylamino; XP(O)(NCO)2 mit X = Hal, Alkoxy, Aryloxy, Alkyl. Aryl; (RO)zP(X)NCO mit R = Alkyl oder Aryl. X = S . NCOR; auDerdem P(O)(NC0)3, P(S)(NCO)3 und P~N~C I~( N H Z ) -NCO (2-Amino-2,4,6,6-tetrachlor-4-isocyanato-l,3,5-tr~~-2,4,6-triphospha~-cyclohexan).
We assume that the AE, mechanism is concerned with cinesubstitution of ( I ) but not of (2). This is because the experimental points lie on a curve for the competition experiments with ( I ) but on a straight line for those with (2); in our experience -admittedly only for EA and AE, substitutionsa mixed mechanism is displayed by non-linear dependence of the molar proportions of the substitution products on the molar proportions of the competing bases, whereas a pure mechanism leads t o linear dependence [2*6,71. Further, reaction of ( I ) with piperidine to yield ( 7 a ) is not inhibited by ethanol whereas the corresponding reaction with (2) is wholly suppressed on addition of ethanol, facts which indicate participation of the AE, mechanism only in the competition experiments with ( I ) . The change from chloride (2) to bromide ( I ) apparently favors the AEa mechanism over the EA mechanism 181. The AEa mechanism was previously demonstrated only for the reaction of piperidine with (10/[9I. This reaction, in which intermediate (12) Recently we reportedrll a simple synthesis of diester isocyanates of phosphoric and thiophosphoric acid (2) by the action of oxalyl chloride on the corresponding diester amides ( I ) . The reaction is effected at 0 OC in an inert solvent such as carbon tetrachloride or benzene.We have now found that isocyanates (3) are also formed by the action of phosgene on diary1 thiophosphoramidates in boiling toluene or chlorobenzene 121.Diary1 phosphoramidates do not react under these conditions. Dialkyl phosphoramidates and thiophosphoramidates do react, even at O°C, but the isocyanates are then formed in only poor yield.Finally we have used organic bases byridine, triethylamine)as HCI acceptors in the reaction of phosphorus(v) amidesproceeding by way of (11) [cf. (S)]. The close resemblance to the "von Richter carboxylation reaction" [lo] (nucleophile: CNS; anionic leaving group: NO: ; hypothetical intermediate: (13); solvent: ethanol) should be pointed out.
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