549. The basic strengths of methylated guanidines

Angyal, S. J.; Warburton, W. K.

doi:10.1039/jr9510002492

Cited by 120 publications

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“…The activity order of the catalysts TBD > TCG > DCOG > MTBD > PMG (Table 3) corresponds to their relative base strength, which is increased by structural factors such as number and type of substituents (cyclic or acyclic chain) 51 . The excellent performance of DCOG and TCG is also assigned to the high symmetry of their guanidinium cations, as observed earlier for the symmetric 1,2,3-trimethylguanidine 65 .…”

Section: Non-ionic Base-catalyzed Processessupporting

confidence: 49%

Transesterification of vegetable oils: a review

Schuchardt¹,

Sercheli²,

Vargas³

1998

J. Braz. Chem. Soc.

980

539

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A transesterificação de óleos vegetais com metanol, bem como as principais aplicações de ésteres metílicos de ácidos graxos, são revisadas. São descritos os aspectos gerais desse processo e a aplicabilidade de diferentes tipos de catalisadores (ácidos, hidróxidos, alcóxidos e carbonatos de metais alcalinos, enzimas e bases não-iônicas, como aminas, amidinas, guanidinas e triamino(imino)fosforanos). Enfoque especial é dado às guanidinas, que podem ser facilmente heterogeneizadas em polímeros orgânicos. No entanto, as bases ancoradas lixiviam dos polímeros. Novas estratégias para a obtenção de guanidinas heterogeneizadas mais resistentes à lixiviação são propostas. Finalmente, são descritas várias aplicações para ésteres de ácidos graxos, obtidos por transesterificação de óleos vegetais.The transesterification of vegetable oils with methanol as well as the main uses of the fatty acid methyl esters are reviewed. The general aspects of this process and the applicability of different types of catalysts (acids, alkaline metal hydroxides, alkoxides and carbonates, enzymes and non-ionic bases, such as amines, amidines, guanidines and triamino(imino)phosphoranes) are described. Special attention is given to guanidines, which can be easily heterogenized on organic polymers. However, the anchored catalysts show leaching problems. New strategies to obtain non-leaching guanidine-containing catalysts are proposed. Finally, several applications of fatty acid esters, obtained by transesterification of vegetable oils, are described.

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Section: Non-ionic Base-catalyzed Processessupporting

confidence: 49%

Transesterification of vegetable oils: a review

Schuchardt¹,

Sercheli²,

Vargas³

1998

J. Braz. Chem. Soc.

980

539

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“…There is the pKa value of 23.3 (10) in acetonitrile measured for 1,1,3,3-tetramethylguanidine (TMG), the base of almost the same strength as DBU. The corresponding values for this compound in water, p~F 2° = 13.6 (15), and in 50% aqueous ethanol, pK, = 13.3 (16), were reported. These data give the difference in pKa values ApK$N-H20 = 9.7.…”

Section: Resultsmentioning

confidence: 99%

Basicity of substituted 2-phenyl-1,1,3,3- tetramethylguanidines and other bases in acetonitrile solvent

Leffek¹,

Pruszyński²,

Thanapaalasingham³

1989

Can. J. Chem.

108

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A series of 30 phenyl substituted derivatives of 2-phenyl-l,l,3,3-tetramethylguanidine was synthesized and the pKa value of each was measured in acetonitrile using a conventional, general purpose glass electrode. The slope of the Hammett relationship, for the para and meta substituted compounds, p = 2.18 + 0.16, is significantly lower than p = 2.85 * 0.06 found for anilines in water, even though the phenyl ring is attached directly to the basic centre in both cases. The influence of electronic and steric effects on the basicity of the compounds is discussed. The solvent effect on the basicity is also discussed, by comparison of the pKa values in acetonitrile and water. The mean value of Ap~tN-H20 = 8.1 + 0.5 is slightly higher than the value previously observed for ammonia and aliphatic amines, A p~p -H 2 0 = 7.5 * 0. On a synthCtisC une skrie de 30 phtnyl-2 tttramCthyl-1,1,3,3 guanidines substitutes sur le noyau phCnyle et, utilisant une electrode de verre conventionnelle d'usage general, on a mesure les valeurs de leur pK, dans llacCtonitrile. Lapente de la relation de Harnmett, pour les composCs substituks en mPta et en para, p = 2,18 0,16, est beaucoup plus faible que la valeur de p = 2,85 2 0,06 qui a kt6 observee pour les anilines dans l'eau, m&me si le noyau phtnyle est attache directement au centre basique dans chacun des cas. On discute de I'influence des effets sttriques et electroniques sur la basicit6 des composCs. En se basant sur une comparaison des valeurs des pKa dans l'acttonitrile et dans l'eau, on discute aussi de I'effet du solvant sur la basicit&. La

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“…The effects of substituents on the baslCity of guanidine have been studied by Davis and Elderfield [21], Hall and Sprinkle [22], Wheland and eowork.ers [23], and Angyal . ~nd Wa~'burton [24]. The high basicity of guamdme, whIch.…”

Section: Discussionmentioning

confidence: 99%

Comparative strengths of four organic bases in benzene

Davis¹,

Hetzer²

1952

J. RES. NATL. BUR. STAN.

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S pectrophotometric studies have shown that t he rea ction of t he base 1,3-di-o-tolylguanidine with t he acidic indicator dye bromopht halein magenta E (tetrabromop he nolphthalein eth yl ester ) in ben zene a t 25° C, like t he reaction s of 1,3-diphe nylguanidine and 1,2,3-tripheny lgua nidine with the same indi cator , can be represen ted by t he following t wo eq ua tions:For ditolylguanidine, lhe equilibrium co nsta n ts Kl a nd K 2 for the firs t a nd seconcil'eactions, respectivcly, arc cst imated to be 1.1 X I06 a nd 6.4. Th ese valucs are co mpa red wi t h val ues for K l a nd K2 prcviously found for di-and t riphe ny lguallidin e and t he value of K l found for t ri e t hylamin e. Th e values for K1, wh ich mea sure th e relative t ende ncies of t he bases to form sa lts with the indi cato r ac id in be nze ne, would be expected to parallel t he ionic dissociation co nsta n ts of t he bases in water. H O\\'ever , t h e parall elism is not good. Diphenylguanidin e and d itolylgua liidinc, which are presumed to b i! weaker bases in wa tc r than t rieth ylamine, are m u ch more reactive in bcnzene. The resul ts demon s t rate how misleadin g t he aq uco uR d issociatio n co nstants may be as a gage of t he relat iv e reactivitics of bases in a nonaq ueo lls SO"'Cll t sll ch as bcnzcnc . Ste ri c a nd solv ation effects ar e di scusscd .

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549. The basic strengths of methylated guanidines

Cited by 120 publications

References 0 publications

Transesterification of vegetable oils: a review

Transesterification of vegetable oils: a review

Basicity of substituted 2-phenyl-1,1,3,3- tetramethylguanidines and other bases in acetonitrile solvent

Comparative strengths of four organic bases in benzene

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