Browsing by Author "Modro, Tomasz A"
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- ItemOpen AccessIntra- and intermolecular reactivity of organic diacyl systems(1988) Symes, Jillian Ellis; Modro, Tomasz AThe mechanism or a thermal amino group transfer-fragmentation reaction yielding carboxyamides from mixed phosphoric-carboxylic anhydrides (RO(R¹R²N)P(O)OC(O)R³; R = R¹ = alkyl; R² = H, alkyl, aryl; R³ = alkyl, aryl) was elucidated from structure reactivity studies using a model system, R = R¹ = R² = Me, R³ = Ph. Kinetic data was obtained using ¹H nmr spectroscopy; MNDO molecular orbital and molecular mechanics calculations, and the crystal structure or N-methyl-2-benzoyloxy-2-oxo-1, 3, 2-oxazaphosphorinane (Pna2₁; a = 22.229(6)Å, b = 7.597(2)Å, c = 7.210(2)Å; v = 1217.6(6)ų. Final R = 3. 08% for 1037 reflections with I (rel )> 2αI (rel) and 15 7 parameters) were userul in providing additional in formation about the reaction mechanism .
- ItemOpen AccessReactivity studies of phosphoric amides and esters(1984) Davidowitz, Bette; Modro, Tomasz AThe effect of protonation and Lewis acid-base interaction on the ¹H n.m.r. chemical shifts of the ester and amide bonds in selected phosphoramidates (RO)₂P(O)NR'₂ was investigated. The results are interpreted in terms of the interaction of the phosphoryl oxygen atom with Lewis acids and oxygen/nitrogen diprotonation in trifluoromethanesulphonic acid. Intramolecular nucleophilic displacement of the halide ion from secondary β-chloroethyl-substituted phosphoramidates X₂P(O)NHCH₂CH₂Cl, diamidates (RO) (MeNH)P(O)NHCH₂CH₂Cl and β-chloroethyl phosphates Y(MeO)P(O)OCH₂CH₂Cl, was studied under conditions of electrophilic (Ag+) and basic (NaH) catalysis. 1,3-Substitution by the nitrogen atom of the phosphdramidates, yielding ethylenimine derivatives was found to be the preferred reaction-pathway; the alternative 1,5-reaction involving the amide nittogen or phosphoryl oxygen atoms was not observed. No intramolecular nucleophilic displacement occurred in the β-chloroethyl phosphate esters.
- ItemOpen AccessThe structure and reactivity of N-Acyl phosphoric amides and related systems(1983) Mizrahi, Valerie; Modro, Tomasz ATwo synthetic approaches towards the N-acyl phosphylamide system Z₂P(O)-NR-C(O)R' (1; Z =alkyl, O-alkyl; R = H, Me; R' =M e, Ph), from phosphylamide and carboxamide precursors are discussed. The infrared, ¹H and ¹³C NMR spectral features of system (1), indicate predominant resonance interaction of the nitrogen non-bonding electrons with the adjacent carboxyacyl, rather than phosphacyl centre. The electron-with- drawing effect of the phosphyl substituent Z₂P(O), is nonetheless sub- stantial, thus weakening the basicity and nucleophilicity of the nitrogen atom and enhancing the electrophilicity of the carbonyl centre. The influence of the electronic distribution within the OPNCO moiety upon the structure and reactivity of (1), has been investigated.
- ItemOpen AccessStructure and synthesis of some phosphorus compounds of potential biological activity(1988) Kyriacou, Panos; Modro, Tomasz A; Paterson-Jones, Colin J
- ItemOpen AccessSyntheses of selected mono- and di-esters of phosphoric acid and stability constants of their copper (II) complexes(1984) Armstrong, Moira Margaret; Modro, Tomasz A; Linder, P W; Torrington, R GA number of different routes were attempted to the syntheses of organic phosphate models (R₁O)(R₂O)PO; where R₁ = 4-nitrophenyl group and R₂ = benzyl, 2-pyridylmethyl, 1-naphthylor 8-quinolyl group. However, preparative difficulties and side reactions, due mainly to the susceptibility of the 4-nitrophenoxy moiety to nucleophilic displacement reactions, resulted in simplification of the target models to a pair of monoesters (R₃O)PO₃H₂ and a pair of diesters (R₃O)(R₄O)P(O)O⁻Na⁺ where R₃ = 1-naphthyl group (monoester (A) or diester (C)) or 8-quinolyl group (monoester (B) or diester (D)) and R₄ = methyl group. Such a set of substrates allowed comparison of the reactivities of phosphate monoesters and diesters and as the components of each pair differed only by the presence or absence of a tertiary amine function in one of the ester linkages, the effect on the reactivity of such a compound, due to the presence of a heterocyclic atom, could be gauged. Complex formation between ligands (A), (B), (C) and (D) and copper(II) ions in aqueous solution at 25° C and I = 0,15 mol dm⁻³ (Na)[Cl⁻] was investigated by means of glass electrode potentiometry and computational analysis. Mononuclear and hydroxo complexes were found to occur with ligands (A), (B) and (D). No complexation was detected with ligand (C). The copper(II) ion was found to be only singly coordinated to ligands (A) and (D) through a terminal phosphate group and the quinolyl nitrogen respectively,while with ligand (B) a chelate structure was formed involving the quinolyl nitrogen and a terminal phosphate group to form a seven-membered ring. Formation constants are given for two protonation and four copper(II) complexes of ligand (B) and for one protonation and four copper(II) complexes, each, of ligands (A) and (D).
- ItemOpen AccessSynthesis and reactivity of some β-substituted alkylphosphonates(1986) Pearce, Madeleine Anne; Modro, Tomasz AThe ability of the β-trimethylammonioethylphosphonic acid dianion to undergo fragmentation in alkaline conditions to produce trimethylamine, ethylene and metaphosphate was investigated. The results obtained were to give an indication of the susceptibility of (C₆H₃Cl₂)OCH₂CH₂N⁺R₂CH₂CH₂P(OR')O₂⁻ to analogous fragmentation to release 2-(3,4- dichlorophenoxy)ethyldialkylamine and ethylene, both well documented plant growth regulating hormones. Since the trimethylammonioethyl-substituted species was found to be stable to fragmentation, studies were embarked upon to convert this molecule into one which would react as required. The substitution of an alkyl group at the β-position of such a β-substituted alkyl phosphonate is reported to accelerate the rate of fragmentation. β-trimethylammoniopentylphosphonate was therefore expected to fragment where its ethyl analogue did not. Attempts at its synthesis were made by various approaches. 2- chloropentylphosphonic acid, a precursor, was successfully prepared and esterified (in order to protect the acid from premature fragmentation) so that it might be reacted with trimethylamine (a nucleophile), to produce diethyl β-trimethylammoniopentylphosphonate, which was then to be hydrolysed to the phosphonic acid form. Instead of the required substitution of Cl by Me₃N, the action of base on the ester produced diethyl 1-pentenylphosphonate. Only traces of the substitution product were observed. It was thought that the replacement of chlorine by a better leaving group such as bromine or iodine would favour the substitution product over the elimination product. Attempts at the synthesis of diethyl 2-iodopentylphosphonate and diethyl 2-bromopentylphosphonate by various means are described, but no satisfactory syntheses have been achieved, since once again the dehydrohalogenation product predominates. During an attempted synthesis of diethyl 2-iodopentylphosphonate by reaction of diethyl 2-chloropentylphosphonate with NaI, an unusual interaction between the sodium cation and the substrate in acetone solution was discovered. Evidence gleaned from ¹H, ¹³C and ³¹P nmr experiments points to the formation of a loose complex between the phosphonate part of the substrate and Na⁺. This phenomenon is also observed when other salts such as CaI₂, KSCN and NaClO₄ are present in solution.
- ItemOpen AccessTertiary N-acyl phosphoramidates : a mechanistic study of their formation and collapse in reactions with nucleophiles(1983) Hendrickse, Theodore Franklin; Modro, Tomasz ADifferent synthetic approaches to tertiary mixed phosphoric-carboxylic imides(III) are discussed. The preparation of (III) via the N-acylation of phosphoramidates was investigated. The reaction of PhC(O)X (X = Br, Cl, F) with the conjugate base of (EtO)₂P(O)NHMe (IX) yields three products: PhCO₂Et (4), PhC(O)NHMe (5) and (PhCO)₂NMe (6). (5) and (6) are formed via the initial rapid formation of (EtO)₂P(O)-NMe-C(O)Ph (IIIe), while (4) results from the E1cB related reaction of (EtO)₂P(O)NMe involving electrophilic assistance by PhC(O)X. The attack of various nucleophilic species at the mixed-imide (IIIe) was studied, and the possible mechanisms of the P-N bond cleavage, followed by the N-methyl transfer from the phosphoryl to the carbonyl centre are discussed.