Hans Cerfontain

University of Amsterdam, Amsterdamo, North Holland, Netherlands

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Publications (269)182.37 Total impact

  • Peter de Wit, Hans Cerfontain
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    ABSTRACT: The sulfonation in 98.5% H2SO4 at 25.0 °C of naphthalene-1-sulfonic acid yields 58% 1,5-, 32% 1,6-, and 10% 1,7-disulfonic acids and that of the 2-sulfonic acid 4% 1,3-, 74% 1,6-, 18% 1,7-, and 4% 2,6- + 2,7-disulfonic acids. Further sulfonation of the latter disulfonic acid mixture in 105.2% H2SO4 at 25.0 °C yields 78% 1,3,6- and 12% 1,3,5- + 1,3,7-trisulfonic acids. Reaction of naphthalene-1,5-disulfonic acid with 105.2% H2SO4 at 25 °C yields 5-sulfonaphthalene-1-sulfonic anhydride.Partial rate factors for the sulfonation of naphthalene-1- and -2-sulfonate in highly concentrated aqueous sulfuric acid (where the sulfonating entity is H2S2O7) are reported. They are discussed in terms of the difference in the reactivity of the α- and β-positions of the naphthalene skeleton and the electronic and steric effects of the sulfonate substituent already present.
    Canadian Journal of Chemistry 02/2011; 61(7):1453-1455. · 1.01 Impact Factor
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    Peter De Wit, Hans Cerfontain, Alfred Fischer
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    ABSTRACT: The mono- and di-sulfonation of the 1,8-alkano- and 1,8:4,5-dialkano-naphthalenes 1–5 with SO3 in dioxane and nitromethane as solvent have been studied and the results compared with those of 1,8-di- (6) and 1,4,5,8-tetramethylnaphthalene (7). The most reactive position of 1,8-ethano- (1), 1,8-propano-naphthalene (2), and 6 is the 4-position. Sulfonation adjacent to the 1,8-ethano bridge can be effected with SO3 in dioxane as reagent, whereas sulfonation ortho to the longer alkano bridges requires the more reactive reagent SO3 in nitromethane. Disulfonation of the1,8:4,5-dialkanonaphthalenes 3–5 leads to the predominant formation of the "noncrossed" (i.e. the 2,7-) disulfonic acid due to the substituent effect of the 2-sulfonic acid group. The isomer distribution data for the sulfonation of the arenes and their monosulfonic acids show that the steric hindrance increases in the order ethano propane ≤ butano and propane < peri dimethyl.
    Canadian Journal of Chemistry 02/2011; 63(8):2294-2297. · 1.01 Impact Factor
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    ABSTRACT: This report describes the synthesis of β-hydroxy esters in good yields by reaction of α-aryl substituted ketones and phenylethanal with lithium methyl acetate and derivatives as anionoid reagents. The incomplete substrate conversion is ascribed to the enolate formation of the α-aryl carbonyl compounds, which concurrent reaction is negligibly small with aliphatic carbonyl compounds. The conversion of β-tetralone with lithium methyl acetate has been examined in some detail.
    Canadian Journal of Chemistry 02/2011; 62(11):2202-2205. · 1.01 Impact Factor
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    ABSTRACT: This study describes a method using 17O nmr to determine the intercarbonyl dihedral angle in a homologous series of seven 1,2-diketones. It is shown that the 17O nmr shifts of the 1,2-diketones are linearly dependent on both the electron density at the oxygen atoms and the n→π* excitation energy of the 1,2-diketo chromophore. Reduction of the overlap in the π system of the 1,2-diketo moiety leads to a gradual upfield shift of the 17O nmr signal, due to the increase in both the π-electron density at the oxygen atoms and the mean transition energy ΔE.
    Canadian Journal of Chemistry 02/2011; 65(9):2234-2237. · 1.01 Impact Factor
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    ABSTRACT: The sulfonation of benzene-SO2X (X = CH3, OCH3, OH, and Cl) and of 1- and 2-naphthalene-SO2X (X = CH3, OCH3, and Cl) with sulfur trioxide in nitromethane as solvent has been studied. In the benzene series, substitution only occurs at the 3-position irrespective of X; the reaction rates, which are all within the same order of magnitude, are low. Upon sulfonation of the 1-SO2X-substituted naphthalenes, the main sulfonation product (58–80%) is the 5-sulfonic acid (5-S); in addition, 6-S and small amounts of 3-S and 7-S are formed. Also, the formation of the intermolecular sulfonic anhydride of 1-(methylsulfonyl)naphthalene-5-S is observed. The 2-SO2X-substituted naphthalenes all yield the 5-S and 8-S in a ratio of For both the benzene and naphthalene series, insertion of SO3 between the SO2 and X moieties of the chlorosulfonyl and methoxysulfonyl substituents proper takes place. In the benzene series these reactions are fast as compared with the actual ring sulfonation, whereas in the naphthalene series they are, in general, relatively slow. In the naphthalene series the mesomeric directing effect of the SO2X groups is less important than in the benzene series; the "naphthalene α-effect" also plays an important role.
    Canadian Journal of Chemistry 02/2011; 71(2):210-215. · 1.01 Impact Factor
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    ABSTRACT: The reaction of sulfur trioxide with benzene, the four halogenobenzenes, and six halogenonaphthalenes in dichloromethane as solvent, and with four chlorinated anthracenes in nitromethane as solvent, has been studied by analysis of the resulting mixture of the sulfo derivatives with 1H NMR. The sulfonation of benzene yields initially benzenesulfonic acid and subsequently the 1,3-disulfonic acid (1,3-S2). The initial sulfonation of the four halogenobenzenes yields ≥ 98% of the 4-S. Their subsequent sulfonation gives the 2,4-S2 and in the case of fluoro- and iodobenzene also the 2,4,6-S3. Monosulfonation of 1-fluoronaphthalene yields only the 4-S, whereas the three other 1-halogenonaphthalenese yield in addition some 5-S. Further sulfonation on any of the four 1-halogenonaphthalene-4-sulfonic acids yields a mixture of the 2,4-S2 and 4,7-S2, and eventually also some 2,4,7-S3, whereas the 1-halogeno-5-sulfonic acids give the corresponding 5,7-S2. Sulfonation of 2-chloro- and 2-bromonaphthalene yields initially 85% 8-S and 15% 4-S, which are subsequently converted into the 6,8-S2 and 4,7-S2, respectively. On reaction with 1.0 mol-equiv. of SO3, 2-chloroanthracene gives the 9-S, and 9-chloroanthracene gives an 18:82 mixture of the 4-S and 10-S. Both 1,5- and 1,8-dichloroanthracene yield initially the 4-S and subsequently the 4,8-S2 and 4,5-S2, respectively.
    Canadian Journal of Chemistry 02/2011; 72(9):1966-1971. · 1.01 Impact Factor
  • ChemInform 12/2010; 24(49):no-no.
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    ABSTRACT: The UV spectra of the geometric isomers of the α-bis(methoxyimino)alkanes I-8 and the structurally related conjugated (methoxyimino)isoxazolines 11 and 13 all exhibit a ππ* absorption band, of which the maxima with cyclohexane as solvent are between 216 and 268 nm, and 258 and 282 nm, respectively. The differences in λmax are discussed in terms of variations in the degree of inter-iminyl conjugation, as a result of (i) variations in the inter-iminyl dihedral angle due to steric hindrance and (ii) variations in the ring strain and/or the dipolar repulsion of the two methoxyimino moieties, as with the three geometric isomers of the four-membered ring compound 1. The lower λmax of (E,E)-8 compared to (E,E)-4 is ascribed to a lower degree of cross-conjugation of the phenyl group with the planar α-bis(methoxyimino) chromophore in the former compound; the absorption band of (E,E)-8 is, in fact, similar to that of the aliphatic (E,E)-5. The energy of the ππ* absorption maximum of the (E,E)-α-bis(methoxyimino)alkanes appears to be linearly related to that of the corresponding (E)-α-oxo oxime ethers with a slope close to unity, illustrating that the sensitivity for structural variations is very similar for the two types of compounds.X-ray structure analysis showed the O-N = C-C = N-O chromophore of (E,E)-5, (E,E)-8 and the (hydroxyimino)isoxazoline (E)-10 in the crystalline state to be all planar within the limits of detection.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 111(1):41 - 48.
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    ABSTRACT: Following our previous reports on the spectroscopy and photochemistry of methyl ethers of cyclic -oxo oximes, we have now studied a number of o- and p-benzoquinone mono-oxime O-methyl ethers and, for comparison, some corresponding o- and p-benzoquinones. The ground-state electronic structure of o-benzoquinones is described satisfactorily by the sum of the two propenal fragments. The structure of the corresponding (E)- and (Z)-mono-oxime ethers can be described similarly as the sum of the propenal and (E)- or (Z)-(methoxyimino)propene fragments. This method fails when used for the construction of the ground-state electronic structure of the isomeric p-benzoquinones and their mono-oxime ethers.The UV spectra of o-benzoquinone mono-oxime ethers are quite different from those of the parent o-benzoquinones in that the free lying n+ π* absorption of the latter is, for the former, shifted to lower wavelength and apparently hidden under the long-wavelength ππ* absorptions. For the p-benzoquinone mono-oxime O-methyl ether 12, however, the long-wavelength nπ* absorption remains visible.Direct irradiation of the tert-butyl-substituted o-benzoquinone mono-oxime O-methyl ethers (E)-5–(E)-7 dissolved in acetonitrile at λ 350 nm leads (in addition to E-Z isomerization) to the formation of the (E)-azobenzenes 16–19 by dimerization of the respective phenylnitrenes. However, in addition, the 2,4-di-tert-butyl derivative (E)-7 undergoes mainly -hydrogen abstraction, probably from the S1(nπ*) state, leading to subsequent cyclization to the relatively stable dienol (E)-14, which eventually isomerizes thermally to the enone (E)-15. Evidence is presented that (Z)-7 exhibits only Z-E photoisomerization and no photocyclization, as has been observed previously with the saturated six-membered ring analogue. Direct irradiation of the corresponding 3,5-di-tert-butyl-o-benzoquinone (3) at 350 nm leads to decarbonylation with formation of cyclopentadienone 13. Sensitized irradiation of mono-oxime O-methyl ether (E)-7, using 1-acetylnaphthalene and 1-fluorenone as triplet sensitizers and acetonitrile as solvent, leads to E-Z isomerization only with eventual photo-stationary state [E]/[Z] ratios of 0.78 and 0.88, respectively.The p-benzoquinone mono-oxime O-methyl ethers 11 and 12 are photostable against 254, 300 and 350 nm radiation; however, any occurring E-Z isomerization escapes detection for symmetry arguments.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 111(10):438 - 447.
  • Hans Cerfontain
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 104(6):153 - 165.
  • Hans Cerfontain, Jan A. J. Geenevasen
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    ABSTRACT: The photochemistry of 1-acetyl-3-methylbicyclo[1.1.0]butane in various solvents usingλ 254 and 300 nm radiation has been studied. In inert solvents, photoisomerization occurs with formation of 3 and 4 with subsequent photoconversion of 3 into 5. The (3 + 5)/4 ratios are significantly greater forλ 254 than forλ 300 nm radiation, illustrating direct reaction from the π* excited state(s). Additional photoreduction to 6 was observed forλ 300 nm in hydrogen-donating solvents, especially in diisopropyl ether and toluene. In carbon tetrachloride, atλ 300 nm, mainly the HCl addition compound 10 is formed via ketone-photosensitized decomposition of CCl4. Similarly, with methanol, 2-propanol and water as solvent or addendum, the 1,3-addition products 7–9 are obtained. Under all of these conditions, no photoproducts containing the intact bicyclo[1.1.0]butyl group were found, illustrating the high chemical reactivity of this severely strained group.Mechanisms for the formation of the photoisomerization, photoreduction and 1,3-dipolar addition products are proposed.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 105(10):386 - 394.
  • A. J. Prinsen, H. Cerfontain
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    ABSTRACT: The sulfonation of o- and m-xylene in concentrated aqueous sulfuric acid has been investigated. Rates and isomer distributions have been measured. The results are discussed in terms of two sulfonating mechanisms. The isomer distributions at 25.0° for the mechanism with H2S2O7 as sulfonating entity are 45.1 ± 0.4% 3- and 54.9 ± 0.4% 4-substitution for o-xylene, and 14.5 ± 0.6% 2-, 84.3 ± 0.6% 4- and 1.2 ± 0.2% 5-substitution for m-xylene. For the mechanism with H3SO4+ as sulfonating entity these data are 6.5 ± 0.9%, 3- and 93.5 ± 0.9% 4-substitution with o-xylene, and 0.5 ± 0.2% 2-, 98.9 ± 0.4% 4- and 0.6 ± 0.2% 5-substitution with m-xylene. The smaller degree of 3-substitution with o-xylene for the H2S2O7 - as compared with the H3SO4+ - mechanism is mainly due to a difference in entropy of activation. The former mechanism encounters more steric hindrance than the latter on substitution ortho to a methyl group. The experimental partial rate factors for the three isomeric xylenes for the two sulfonation mechanisms differ by less than a factor of 4 from those calculated on the basis of additivity of substituent effects with the exception of the 2-position of m-xylene, for sulfonation by the entity H3SO4+, and of the 2- and 4-positions of m-xylene for sulfonation by the entity H2S2O7.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 88(7):833 - 844.
  • C. W. F. Kort, H. Cerfontain
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    ABSTRACT: Rates and isomer distributions have been determined for the sulfonation of fluoro-, bromo- and iodo-benzene in 83-98% sulfuric acid at 25°. The results are analogous to those for chlorobenzene 1. It is shown that the mechanism proposed previously1 is incorrect The σ-complex formed in the rate-limiting reaction of ArH with H2S2O7 is not
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 88(7):860 - 864.
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    ABSTRACT: The sulfonation of 1- and 2-naphthol with sulfur trioxide in C2H3NO2 has been studied by using 1H NMR. 1-Naphthol (1) yields, upon reaction with 1.0 mol-equiv of SO3, a mixture of 2- and 4-sulfonic acids (2- and 4-S); upon increasing the reaction temperature, the relative amount of 2-S increases. Upon reaction with 4.0 mol-equiv of SO3, the initially observed products are the hydrogen sulfate 1-O,2,4-S3, and some corresponding sulfonic anhydrides. After prolonged reaction times, some 1-O-4,7-S3, is formed.2-Naphthol (3), upon reaction with 1.0 mol-equiv of SO3, yields a 85: 15 mixture of 1-S and 8-S, whereas upon reaction with 2.0 mol-equiv of SO3, a 8: 14: 78 mixture of the 5-S, 6-S and 8-S are formed. Sulfonation of 3, either by (i) reaction with 1.2 and, subsequently, an additional 2.0 mol-equiv of SO3, or (ii) by direct addition of 4.0 mol-equiv of SO3, yields a mixture of the carbyl sulfates 5-5-S and 5-6-S and the hydrogen sulfate 3-O,6,8-S3, the relative yield depending on the method used.The results are discussed in terms of initial formation of the corresponding naphthyl hydrogen sulfates and on the basis of a comparison with the reactions of 1- and 2-naphthyl methanesulfonates, the chosen model compounds for the hydrogen sulfates, with SO3.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 112(3):210 - 215.
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    ABSTRACT: The protonation of phenol (2), 4-fluorophenol (3), phenyl methanesulfonate, potassium phenyl sulfate and the potassium 2- and -4-sulfonates of both phenol and anisole in concentrated aqueous sulfuric acid at 30°C has been investigated using 13C NMR spectroscopy. The results show that phenol and 4-fluorophenol are protonated predominantly on the oxygen atom. This protonation is governed by the H0a acidity function. The pKa of the oxonium ions of 2 and 3 are -6.40 ± 0.05 and -6.41 ± 0.05, respectively. The protonation of phenyl methanesulfonate occurs at acid concentrations > 100%. Potassium phenyl sulfate in ≥20% H2SO4 hydrolyses very rapidly to give phenol. The 2- and 4-sulfonates of both phenol and anisole are protonated on both the -OR (R = H, Me) and the -SO3− groups; the sulfuric acid concentrations of half-protonation have been determined to be between 80.0 and 83.3% H2SO4, corresponding with pKa's of the conjugate acids between -6.34 and -6.66 based on the H0a scale.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 102(6):293 - 298.
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    ABSTRACT: Following our previous reports on the spectroscopy and photochemistry of methyl and ethyl ethers of simple acyclic and non-strained cyclic α-oxo oximes, we have now studied 4-(methoxyimino)-2,2,3,3-tetramethylcyclobutanone (1), of which the ring is severely strained, 3,5,5-trimethyl-4(5H)-isoxazolone (8), of which the (Z)-oxime function is constrained in a five-membered ring, and 6-(benzyloxyimino)-2,2,5,5-tetramethylcyclohexanone (10), which is a benzyl ether. Upon irradiation of (E)-1 with λ 254 nm, the main process is photodissociation, leading to the same type of products as obtained with the six-membered ring homologue 3, but in addition to 2,2,3,3-tetramethyl-4-oxobutanenitrile (13) and 2,2,3,3-tetramethylcyclopropanone O-methyloxime (21). The triplet-sensitized irradiation of (E)-l, in contrast to that of the higher homologues, leads, in addition to E-Z isomerization, to photodissociation, yielding the same photoproducts as obtained after direct irradiation with 254 nm.The 4-isoxazolone 8 is photostable against radiation of 350 and 300 nm. Irradiation of 8 with λ. 254 nm leads to population of the excited singlet ππ* state and subsequent photodecomposition as a result of inital N-O homolysis, the observed products being carbon monoxide, acetonitrile, acetone and small amounts of ethanol. The occurrence of the photodecomposition is in agreement with the theoretical prediction' that the excited singlet ππ* (Z)-α-oxo oxime ethers would give N-O homolysis, provided that the other route of deactivation via Z-E isomerization, which has a much lower energy barrier on the potential energy surface, cannot take place.The photochemistry of the benzyl ether (Z)-10, of which the intercarbonyl-iminyl dihedral angle is approx. 45° and the π systems of the phenyl and the C = N-O moieties are perpendicular to one another, with λ 350, 300 and 254 nm is different from that of the corresponding methyl ether 36 in two ways. Firstly, on using λ 350 and 300 nm decomposition was observed which is, however, slow relative to the Z-E isomerization and, secondly, the photodecomposition products are of a different nature, since the assigned primary and secondary product from 10 are benzaldehyde and 6-(benzoylamino)-2,2,5,5-tetramethylcyclohexanone (32), respectively.Mechanisms have been presented to explain the formation of the photoproducts obtained from 1, 8 and 10.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 110(2):31 - 40.
  • Frank Stunnenberg, Hans Cerfontain
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    ABSTRACT: The photochemistry of the α-bis(methoxyimino)alkanes 1–5 and the, structurally related, conjugated dihydro(methoxyimino)isoxazoles 6 and 7 was studied. Triplet-photosensitized irradiation of 1–7 leads only to stepwise E-Z isomerization. Photostationary-state (pss) ratios for 1,6 and 7 are reported for the various applied triplet sensitizers. Direct irradiation with 254 nm leads to both E-Z isomerization (which is the dominant reaction) and formation of products resulting from initial N-O homolysis of the excited singlet ππ* state. Mechanisms for the formation of the various products are proposed and the relative importance of the various steps is indicated and discussed. For the α-bis(methoxyimino)alkanes 1 and 3, only the (E,Z)-isomer undergoes N-O homolysis. With the (methoxyimino)isoxazolines 6 and 7, only the exocyclic NO bond exhibits homolysis and not the strained endocyclic bond.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 111(2):79 - 87.
  • Hans Cerfontain, A. Koeberg‐Telder
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    ABSTRACT: NMR evidence is presented for complex formation between nitromethane and sulfur trioxide in thrichlorofluoromethane as solvent according to . In addition, kinetic evidence for complex formation between nitrobenzene and sulfur trioxide in trichlorofluoromethane was obtained from sulfonation studies of that system.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 89(6):569 - 574.
  • Hans Cerfontain, Jan A. J. Geenevasen
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    ABSTRACT: The photochemistry of 1-acetyl-3-methylbicyclo[1.1.0]butane in various solvents usingλ 254 and 300 nm radiation has been studied. In inert solvents, photoisomerization occurs with formation of 3 and 4 with subsequent photoconversion of 3 into 5. The (3 + 5)/4 ratios are significantly greater forλ 254 than forλ 300 nm radiation, illustrating direct reaction from the π* excited state(s). Additional photoreduction to 6 was observed forλ 300 nm in hydrogen-donating solvents, especially in diisopropyl ether and toluene. In carbon tetrachloride, atλ 300 nm, mainly the HCl addition compound 10 is formed via ketone-photosensitized decomposition of CCl4. Similarly, with methanol, 2-propanol and water as solvent or addendum, the 1,3-addition products 7–9 are obtained. Under all of these conditions, no photoproducts containing the intact bicyclo[1.1.0]butyl group were found, illustrating the high chemical reactivity of this severely strained group.Mechanisms for the formation of the photoisomerization, photoreduction and 1,3-dipolar addition products are proposed.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 105(10):386 - 394.
  • C. W. F. Kort, H. Cerfontain
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    ABSTRACT: Chlorobenzene has been sulfonated homogeneously in aqueous sulfuric acid varying from 83.4 to 99.6 wt-%, at 25°. The isomer distribution-98.8% para, 0.8% ortho, 0.4% meta - is constant over the acid range studied. The substrate isotope effect has been determined under conditions of rapid hydrogen exchange; kD/kH varies from 0.8 in 95% sulfuric acid to 0.4 in 97%. The dependence of the reaction rate and the isotope effect on the acid concentration is explained by an SE2-mechanism involving attack by H2S2O7 followed by proton removal from the σ-complex by HSO4−; the latter process is partly rate-limiting at high acid concentrations.
    Recueil des Travaux Chimiques des Pays-Bas. 09/2010; 86(8):865 - 872.