The ability of soil samples of pH 4.2, 5.5 and 7.2 to generate gaseous singlet oxygen was investigated using a separated-surface-sensitised reactor. It was found that the soil samples can act as sensitisers for the production of singlet oxygen in a similar fashion to the well known sensitisers chlorophyll and Rose Bengal. The reaction of singlet oxygen so produced with the pyrethroid insecticide, bioresmethrin, has been investigated.

The Rose Bengal sensitised photo-oxidation of bioresmethrin (I), 2-benzylfuran-4-ylmethyl acetate (II), and 2-benzylfuran-4-ylmethanol (III) has been studied in methanol and methanol + water (1 + 1 by volume) solutions by monitoring the rate of oxygen removal from the system. The results indicate that the compounds studied are oxidised via reaction with singlet oxygen. Values for the rate constants for reaction of singlet oxygen with compounds I-III have been determined over the temperature range 293-308 K, and the energy of activation and entropy of activation for the reactions have been determined. The data have been interpreted in terms of the site of attack of singlet oxygen on the compounds.

Photochemical reactions between [Mn2(CO)8L2] (L = CO, PBu3, PEt3, P(OMe)3, P(OPh)3, PPh3) and alkyl halides (RX) yield both alkyl and halo complexes, [MnR(CO)4L] and [MnX(CO)4L], in equimolar quantities. Kinetic and quantum yield studies suggest that these reactions proceed by a radical chain pathway involving CO dissociation from the dinuclear complex and metal—metal bond homolysis of the coordinatively unsaturated dinuclear intermediate.

Equilibrium constants have been measured by n.m.r , spectroscopy for the electron donor- electron acceptor interaction between a number of aromatic hydrocarbons and diazines . The values obtained have shown that the interaction is weak, and that the aromatic hydrocarbon acts as the electron donor and the diazine as the electron acceptor in the systems studied. Chemical-shift data have provided evidence for the relative positioning of the donor and acceptor components within the various complexes. The effect of temperature on the equilibrium constant for complex formation between (1H6)benzene and pyrazine has shown that the enthalpy of formation is close to zero.

AbstractThe products from the methylene blue sensitised photo‐oxidation of 2‐dimethylamino‐5,6‐dimethylpyrimidin‐4‐ol (I) in deuterochloroform/deuteroacetone have been investigated. A zwitterion and a hydroperoxide are formed initially, with the zwitterion predominating. The zwitterion compound degrades or reacts in the solid state on silica gel to give further products.

AbstractThe chlorophyll sensitised photodegradation of 2‐dimethylamino‐5, 6‐dimethylpyrimidin‐4‐ol (I), a hydrolysis product of pirimicarb, in the solid state on silica gel and in chloroform solution has been investigated. The product distribution in the solid state photodegradation was different from that in chloroform solution and was dependent upon the wavelength range of the incident radiation. When radiation of wavelength greater than 420 nm was used, the products formed in the chlorophyll sensitised degradation of I in the solid state were similar to those obtained when Rose Bengal or Methylene Blue were used as sensitisers. These results indicate that singlet oxygen is implicated in the sensitised photodegradation of I in the solid state. Numerous products were formed in each of the systems studied.

2-Dimethylamino -5,6-dimethylpyrimidin-4-ol (I) and 5-n-butyl-2-dimethylamino-6-methylpyrimidin-4-ol (dimethirimol) form 1:1 complexes with Cu(II), Cd(II), Mn(II), Co(II), and Hg(II) salts. The infrared spectra of the complexes indicate that these pyrimidine bases bond to the metal ions through the carbonyl group at C(4).

AbstractThe sensitisation by Rose Bengal of the photo‐oxidation of 2‐dimethylamino‐5,6‐ dimethylpyrimidin‐4‐01 (I) has been studied in aqueous solution by monitoring the rate of oxygen consumption in the system. The results are in accord with a mechanism whereby I is oxidised via a reaction with singlet oxygen. Values for the rate constant for the reaction of I with singlet oxygen have been determined over the temperature range 279‐296 K, and the energy of activation and entropy of activation for the reaction have been evaluated as 71.9 kJ mol−1 and 150.5 J K−1 mol−1, respectively. The positive value for the entropy of activation suggests that the reaction intermediate could have a zwitterionic form. The effect of pH on the reaction rate has been investigated, and the increased rate at high pH has been attributed to an increase in singlet oxygen production as the pH is raised.

AbstractPhotolysis of 2‐dimethylamino‐5, 6‐dimethylpyrimidin‐4‐ol (I) in degassed aqueous solution yields two isomeric photo‐dimers which are formed by dimerisation across the 5, 6‐double bond of I. The yield of dimers is dependent upon the initial concentration of I and on the temperature; this can be explained in terms of a mechanism whereby pyrimidinol aggregates react to give dimers. The formation of aggregates can account for the fact that the quantum yield for the overall reaction of I was higher in degassed acetonitrile than in degassed aqueous solution, it can also account for four photo‐dimers being formed in the former solvent and only two in the latter solvent. The photo‐dimers revert to I when heated or on photolysis. That photodimers are not formed under natural conditions in the environment is considered to be partly because oxygen may react competitively with photo‐excited pyrimidinol species and so prevent dimerisation.

AbstractRate constants have been measured for the reaction in chloroform solution of singlet oxygen with the fungicides ethirimol (5‐butyl‐2‐ethylamino‐6‐methylpyrimidin‐4‐ol) and dimethirimol (5‐butyl‐2‐dimethylamino‐6‐methylpyrimidin‐4‐ol), and with the compounds 2‐dimethylamino‐5,6‐dimethylpyrimidin‐4‐ol, 2‐dimethylamino‐6‐methylpyrimidin‐4‐ol, 4‐benzyloxy‐2‐dimethylamino‐5,6‐dimethylpyrimidine and 2‐diethylamino‐6‐methylpyrimidin‐4‐ol. The values obtained show that singlet oxygen reacts readily with these compounds; the differences between the rate constant values have been rationalised in terms of the different structural features of the compounds studied. The possibility that singlet oxygen may react with agricultural chemicals under natural conditions is considered.

The fluorescence, phosphorescence and absorption spectra of 5,6-dimethyl-2-dimethyl-amino-4-hydroxypyrimidine (1), 5-n-butyl-2-dimethylamino-4-hydroxypyrimidine (2), and 5-n-butyl-2-ethylamino-4-hydroxypyrimidine (3) have been obtained in organic media and in aqueous solution at different pH values. The spectra reveal that the pyrimidines exist principally as cations at low pH, neutral species at pH values around 7 and as anions at high pH. The pK values for the ground state of compounds (1)–(3) have been measured as have the pK* values for the first excited singlet state.

Photolytic decomposition of indapamide (I) in nitrogen-flushed methanol yields 3-sulfamoyl-4-chlorobenzamide (II), 2-methylindoline (III), semicarbazide (IV), and 1-(N-formamido)-2-methylindoline (V); in oxygen-flushed methanol, II--V, 1-aminocarboxymethyl-2-methylindoline (VI), 3-sulfamoyl-4-chlorobenzoic acid (VII), methyl-3-sulfamoyl-4-chlorobenzoate (VIII), and 2-(N-acetamido)-benzoic acid (IX) are formed. A comparison is made with thermal decomposition of I.

Pesticide ScienceVolume 10, Issue 2 p. 171-176 Article Photochemistry of some systemic pyrimidine fungicides† Clifford H. J. Wells, Clifford H. J. Wells School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this authorStephen J. Pollard, Stephen J. Pollard School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this authorDevdoot Sen, Devdoot Sen School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this author Clifford H. J. Wells, Clifford H. J. Wells School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this authorStephen J. Pollard, Stephen J. Pollard School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this authorDevdoot Sen, Devdoot Sen School of Chemical and Physical Sciences, Kingston Polytechnic, Kingston upon Thames, SurreySearch for more papers by this author First published: April 1979 https://doi.org/10.1002/ps.2780100211Citations: 5 † Synopsis of a paper presented at the symposium on Photodegradation of pesticides on 3 October 1978, organised by the Physicochemical and Biophysical Panel (Pesticides Group), Society of Chemical Industry. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume10, Issue2April 1979Pages 171-176 RelatedInformation

AbstractDas Fungicid (I) reagiert bei UV‐Bestrahlung mit einer Mitteldruckquecksilberlampe (300 ‐ 320 nm) unter Dimerisierung zu Gemischen von vier isomeren Cyclobutanderivaten (II), deren Stereochemie der der entsprechenden lß‐Dimethyluracildimeren entspricht.