Efficient S-alkylation of cysteine in the presence of 1,1,3,3-tetramethylguanidine

The synthesis of S-alkylated cysteine derivatives was carried out successfully in the presence of 1,1,3,3-tetramethylguanidine. Alkylation proceeded in high yields on unprotected amino acids and peptides containing a sulfhydryl group.     

Catalytic cyanosilylation of ketones using organic catalyst 1,1,3,3-tetramethylguanidine

1,1,3,3-Tetramethylguanidine acts as a highly effective catalyst for cyanosilylation of various ketones and aldehydes to the corresponding cyanohydrin trimethylsilyl ethers in up to 99% yield. The reaction proceeds smoothly with 0.1 mol % catalyst loading at 25 °C under solvent-free conditions.     

Stable analogs of the uranyl ion containing 1,1,3,3-tetramethylguanidine

The reaction of 1,1,3,3-tetramethylguanidine (HTMG) with [UO(2)Cl(2)(THF)2] yielded [UO(2)Cl(2)(HTMG)2] 1, the first uranyl tetralkylguanidine adduct reported, further investigation led to the synthesis of [UO(2)(DBP)2(HTMG)2] 2 and [UO(2)(DBP-4-Me)2(HTMG)2] 3 via the reaction of [UO(2){N(SiMe(3))2}2(THF)2] with HTMG and the appropriate aryl alcohol, HO-2,6-(t)Bu(2)-4-RC(6)H(2) (R = H, DBP; R = CH(3), DBP-4-Me).     

Contributions to the chemistry of halosilane adducts: XVIII. On the nature of compounds of trimethylhalosilanes with 1,1,3,3-tetramethylguanidine and 2-trimethylsilyl-1,1,3,3-tetramethylguanidine: preparation and characterization of mono- and bis-(2-trimethylsilyl)-1,1,3,3-tetramethylguanidinium halides

1,1,3,3-Tetramethylguanidine (TMG) and 2-(trimethylsilyl)-1,1,3,3-tetramethylguanidine (TMSTMG) react with trimethylhalosilanes Me₃SiHal in equimolar ratio with ionization of the Sihalogen bond to give the stable guanidinium salts [(Me₂N)₂CNHSiMe₃]Hal (Hal  Cl (1), Br (2)) and [(Me₂N)₂CN(SiMe₃)₂]Hal (Hal  Cl (3), Br (4), I (5)), respectively, involving tetracoordinate silicon. No reaction occurs with Me₃SiF. The same ionic species are present in CHCl₃ or CH₃CN solutions (IR, ¹H, ²⁹Si NMR), thus establishing for the first time, the formation of an ionic solid derivative of Me₃SiCl stable towards dissociation. Reaction with an excess of TMG gives an equilibrium mixture of TMSTMG and TMG · HHal. The bis(silyl)guanidinium salts are less stable towards dissociation than the mono(silyl) derivatives, the stability sequence being Cl⁻ < Br⁻ < I⁻ within the series. The reactions of both types of compound have been investigated. The implications of the present and earlier results for the mechanisms of racemization and nucleophilic substitution at silicon are discussed.     

Synthesis and structural characterization of geminal and non-geminal 1,1,3,3-tetramethylguanidine substituted derivatives of cyclotriphosphazene: Thermal and spectroscopic investigations of the products

Abstract

The reactions of hexachlorocyclotriphosphazene, N₃P₃Cl₆ (1) with 1,1,3,3-tetramethyl-guanidine (2) in (1:1:2, 1:2:4 and 1:3:6) stoichiometries in THF and dichloromethane solutions under reflux yield a total of 4 novel products: three non-geminal derivatives, N₃P₃Cl₄[NCN₂(CH₃)₄]₂ (3), N₃P₃Cl₃[NCN₂(CH₃)₄]₃ (4) and N₃P₃Cl₂[NCN₂(CH₃)₄]₄ (5); and one hexa-substituted product, N₃P₃[NCN₂(CH₃)₄]₆ (6). The structures of 3-6 have been determined mainly by elemental analysis, MS, ³¹P and ¹H NMR spectral data. Furthermore, thermal characteristics of the synthesized compounds 4 and 6 were evaluated using Differential Scanning Calorimetric (DSC) measurements. NMR spectroscopic data, product types and relative yields are compared with those of the previously investigated derivatives of N₃P₃Cl₆ (1) with mono and difunctional reagents.     

The reactions of non-gem-hexanedioxytetrachlorocyclotriphosphazene with 2-(2-hydroxyethyl)thiophene,benzyl alcohol and 1,1,3,3-tetramethylguanidine. Spectroscopic studies of the derived products

Abstract

Reactions of non-gem-hexanedioxytetrachlorocyclotriphosphazene (1) with monofunctional nucleophilic reagents, 2-(2-hydroxyethyl)thiophene (2), benzyl alcohol (3) and 1,1,3,3-tetramethylguanidine (4) were investigated. The reactions, using an excess of NaH, in THF solutions, under refluxing conditions and with 1:2?mole ratios allow the synthesis of the following novel cyclotriphosphazene derivatives: 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-[2-(2-ethoxy)hiophene]-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-(C₆H₈OS)₂] (5); 2,4-(hexane-1,6-dioxy)-2,4,6,6-[2-(2-ethoxy) thiophene]-cyclotriphosphazatriene, N₃P₃[O(CH₂)₆O-(C₆H₈OS)₄] (6); 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-(methoxybenzene)-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-(C₆H₅CH₂O)₂] (7); 2,4-(hexane-1,6-dioxy)-2,4,6,6-(methoxybenzene)-cyclotriphosphazatriene, N₃P₃[O(CH₂)₆O-(C₆H₅CH₂O)₄] (8); and 2,4-dichloro-2,4-(hexane-1,6-dioxy)-6,6-(1,1,3,3-tetramethyguanidine)-cyclotriphosphazatriene, N₃P₃Cl₂[O(CH₂)₆O-HN-CN₂(CH₃)₄] (9). The structures of the synthesized compounds (5–9) have been characterized by elemental analysis, TLC-MS, ¹H, ¹³C and ³¹P {+¹H} and {?¹H} NMR spectral data.     

Microtitration of weak organic acids in nonaqueous solvents

Summary The applicability of nonaqueous titrimetry to the microdetermination of weak organic acids has been established.Phenols have been found to be titrable in dimethylformamide. Those containing one or more chlorine, hydroxyl, or carbonyl groups can be titrated to a thymol blue endpoint and those containing amino or alkyl groups to an azo-violet endpoint.Sulfonamides, barbiturates, enols, imides, and some hydrazides have also been titrated in dimethylformamide. The scope extends to compounds with a pK_a of about 9 for visual titrations and 10.5 for potentiometric titrations in dimethylformamide.Pyridine may be used as a solvent for the visual titration of weak acids with pK_a of up to about 10.5. Methyl-isobutanone may be used for the visual titration of acidic compounds with a pK_a of about 9 and lower by using thymol blue as the indicator.The hydrazides give better results in potentiometric titrations; the visual endpoints are poorly defined for practical purposes.

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Zusammenfassung Die Maßanalyse in nichtwäßrigem Milieu wurde für die Mikrobestimmung schwacher organischer Säuren herangezogen.Phenole lassen sich in Dimethylformamid titrieren. Enthalten sie ein oder mehr Chloratome bzw. Hydroxyl- oder Carbonylgruppen, so können sie gegen Thymolblau als Indikator titriert werden; Amino- oder Alkylgruppen tragende Phenole werden gegen Azoviolett titriert.Sulfonamide, Barbiturate, Enole, Imide und einige Hydrazide werden gleichfalls in Dimethylformamid titriert: Verbindungen mit einem pK_s bis etwa 9 durch visuelle Endpunktbestimmung, bis 10,5 auf potentiometrischem Weg.Pyridin eignet sich als Lösungsmittel für die visuelle Titration schwacher Säuren mit einem pK_s bis etwa 10,5, Methylisobutanon hingegen für saure Verbindungen mit einem pK_s von etwa 9 und weniger, wobei Thymolblau als Indikator dient.Hydrazide werden besser potentiometrisch titriert; die visuelle Endpunktbestimmung eignet sich für praktische Zwecke nur wenig.

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Rèsumè La possibilité d'application de la titrimétrie non aqueuse au microdosage des acides organiques faibles a été établie par les auteurs. Ils ont trouvé que les phénols étaient susceptibles d'être titrés dans la diméthylformamide. Ceux qui contiennent un ou plus d'un groupement chlore, hydroxyle ou carbonyle peuvent être titrés en présence de bleu de thymol comme indicateur de point final, et ceux qui contiennent des groupements amines ou des groupements alcoyles à l'aide de l'indicateur violet azoïque. Les sulfamides, les barbiturates, les énols, les imides et quelques hydrazides ont été également titrés dans la diméthylformamide. Le domaine de dosage s'étend à des composés dont le pK_a est voisin de 9 pour les titrages visuels et de 10,5 pour les titrages potentiométriques dans la diméthylformamide. Il est également possible d'utiliser la pyridine pour les titrages visuels d'acides faibles dont le pK_a est voisin de 10,5. On peut employer la méthylisobutanone pour des titrages visuels de composés acides dont le pK_a est inférieur à 9 ou voisin de cette valeur; on utilise alors le bleu de thymol comme indicateur.Il est préférable d'utiliser les titrages potentiométriques dans le cas des hydrazides car les points finaux de titrages sont mal définis dans la pratique courante lorsqu'on les détermine visuellement.

     

Electrochemical cyclization of tetramethyl esters of 2-substituted propane-1,1,3,3-tetracarboxylic acids in the presence of salts of hydrohalic acids

The chemical and electrochemical cyclization of tetramethyl esters of 2-substituted propane-1,1,3,3-tetracarboxylic acids in the presence of hydrohalic acid salt mediators were studied. It was found that the chemical variant of the cyclization of the corresponding ,'-dianions of esters of propane-1,1,3,3-tetracarboxylic acids by the action of iodine or bromine is substantially inferior to the electrochemical variant. In the latter case, the esters of substituted cyclopopane-1,1,2,2-tetracarboxylic acids are formed in a 87–98% yield. The tetramethyl ester of 2-isopropylpropane-1,1,3,3-tetracarboxylic acid, which under the electrolysis conditions decomposes according to a Michael retroreaction is an exception.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2783–2789, December, 1990.     

Electrochemical cyclization of esters of propane-1,1,3,3-tetracarboxylic acids to give esters of substituted cyclopropane-1,1,2,2-tetracarboxylic acids

Conclusions Esters of substituted propane-1,1,3,3-tetracarboxylic acids cyclize to give high yields of esters of substituted cyclopropane-1,1,2,2-tetracarboxylic acids upon electrochemical oxidation in methanol in the presence of sodium iodide as an electron transfer catalyst.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 228–230, January, 1987.     

New Techniques in Electrometric Titrations

Five new techniques in electrometric titration are described: 1.Oscillopolarographic titration without incision at 1 micro and 1 macro Pt electrodes.2.Oscillopolarographic titration without in -cision at 3 electrodes.3.Oscillo potentiometric titration at 3 electrodes.4.Zero current oscillo bipotentiometric titration.5.Alternating current oscillo bipotentiometric at 2 similar electrodes.Among them methods 1,4,5 are very useful.     

Thermodynamic properties of weak acids involved in enzyme-catalyzed reactions

Measurements of apparent equilibrium constants and transformed enthalpies of enzyme-catalyzed reactions are making it possible to obtain delta(f)G degrees and delta(f)H degrees of species of biochemical reactants in dilute aqueous solution that could never have been determined classically. This article is concerned with the pKs that determine the pH dependencies of the standard transformed thermodynamic properties of biochemical reactants. The database BasicBiochemData3 makes it possible to calculate 82 pKs of 60 reactants as functions of ionic strength at 298.15 K. Standard enthalpies of formation of all the species are known for 27 of these reactants, and so their pKs can be calculated as functions of temperature and ionic strength. This article also presents calculations of delta(r)G degrees, delta(r)H degrees, and delta(r)S degrees at 298.15 K and three ionic strengths for the 42 pKs of these 27 reactants.     

Titrations with piezoelectric monitoring : Part 1. Fundamental theory and titration of acids and bases

The use of a piezoelectric quartz crystal detector is proposed for monitoring the course of a titration reaction by observation of the frequency shift of the oscillating crystal. Satisfactory titrations can often be obtained using the acid-base technique, which is much more sensitive than the classical conductimetric titration and oscillometric titrration, with a lowest titratable concentration that is much lower but which can still be applied in the presence of a large amount of unreacting electrolyte.     

Enhancement of conductometric detection of weak acids in ion chromatography

Anions of weak acids can represent a problem when determined via chemically suppressed ion chromatography as the acids can be weakly ionised, giving low conductivity and hence low sensitivity. Previous work showed that converting some weak acids back to their sodium salts, using a second micromembrane suppressor, greatly enhanced conductivity and thus sensitivity. This paper will discuss further work in optimising the conversion for boric acid by using sodium salts of EDTA and the mechanisms involved.     

Interaction of non-ionic hydrogels with weak aromatic acids

Measurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid-base titration that the PNIPA/water system may exhibit a slight ion exchanging character.     

Titrations of sulphonamides in cationic micellar systems

A titrimetric determination of some sulphonamides with 0.1 M sodium hydroxide in the presence of hexadecylpyridinium chloride is described. Potentiometric titrations are slow; visual titrations are satisfactory. The pK_a shift can be interpreted in the light of general micellar behaviour.     

Statistical evaluation of mobility curves of univalent weak acids

This paper brings a new rigorous and complete statistical approach to the data processing of the mobility curves of univalent weak acids. It is based on a fundamental equation for the mobility curve, on applying the mathematical principle of the best fit, derivation of the related nonlinear equation and finding the mathematical solution of it which gives the best estimates of the mobility curve parameters. The mathematical procedure presented here does not impose any limitations upon the numerical data used, i.e., the experimental values of mobilities and pH may be real numbers (positive, negative, zero). Further, rigorous explicit statistical formulas are derived for SDs of effective mobility, dissociation constant, and ionic mobility of fully ionized anion in question.