A Study of the Mechanism and Kinetics of the Thioacetamide Hydrolysis Reaction<sup>1</sup>

Rosenthal, Donald; Taylor, T.I.

doi:10.1021/ja01568a007

Cited by 63 publications

(18 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In strong sulphuric acid these are replaced by a single peak a t about 240 mp (Table I) which may be the .rr -+ a* peak shifted to longer wavelengths by protonation (12), the blue shift of the n --t u* peak (11) caused by protonation having taken it out of the observable region of the spectrum. These spectral changes are very similar to those already observed for thioacetamide (11,13).…”

Section: Resultssupporting

confidence: 87%

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Edward¹,

Stollar²

1963

Can. J. Chem.

View full text Add to dashboard Cite

The ionization in aqueous sulphuric acid of thiolactams consisting of five-, six-, and sevenmembered rings has been studied. With increasing concentration of acid the ionization ratio increases more rapidly than ho. A possible explanation involving the hydration of the thiolactam is given. Changes in the basicity of thiolactams with ring size parallel changes previously found for lactams.By analogy with the resonance structures of simple amides (I), the structure of lactams (I; X = 0 ) would be expected to be made up by a 60y0 contribution from structure Ia (X = 0 ) and 40% contribution from structure Ib (X = 0), although the relative weights of the contributions could be altered somewhat by ring strain (2). Thiolactams (I; X = S) have higher dipole moments (3), and so should be represented to a preponderant extent by the dipolar form I b (X = S). The high polarity of the thiolactams (I; X = S, n = 3 , 4 , and 5) may in part account for the fact that they are solids a t room temperature while the corresponding lactams (I; X = 0, n = 3, 4, and 5 ) are liquid, and that (as postulated later in this paper) they appear to be more extensively hydrated in a-queous solution than are the lactams.It is probable that lactams and thiolactams in strong acid are protonated on the oxygen or sulphur atom to give the conjugate acids (11; X = 0 or S) (4). Consequently i t became of interest to compare the basicities of the two classes of compounds. I t seemedpossible that in spite of the greater intrinsic basicity of oxygen as compared with sulphur (cf. OH-and SH-), the greater negative charge on the sulphur of thiolactams would cause them to be more basic than lactams. We have accordingly determined the protonation constants of the thiolactams (I; X = S, n = 3, 4, and 5) for comparison with the protonation constants reported for the lactams (I; X = 0 , n = 3, 4, and 5) (2).

show abstract

Section: Resultssupporting

confidence: 87%

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Edward¹,

Stollar²

1963

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…These are the hydrolysis of several amides (154), the hydrolysis of thioacetamide (155) and the hydrolysis of CHaHgI (156).…”

Section: Acidity Functionsmentioning

confidence: 99%

Physical Organic Chemistry

Taft¹,

Deno²,

Skell³

1958

Annu. Rev. Phys. Chem.

View full text Add to dashboard Cite

A reasonable definition of the domain of Physical Organic Chemistry was given seventeen years ago by L. P. Hammett, in his inspiring book by this title, as one concerned with investigations of organic chemistry by quanti tative and mathematical methods. The chief directions of the field were given as (a) mechanisms of reactions, and (b) the effects of structure and environment on reaction rates and equilibria.The amount of significant research reported during the current year which falls within these confines has been so enormous that it early became apparent to us that to cover such an area would scarcely enable us to prepare a running list of titles. Consequently we have chosen for detailed review only four admittedly narrow topics within the realm. In so doing it is our hope that our modest efforts at review will provide something of use to those interested in our topics. No claims are made as to the relative merits of topics considered or not considered, and we trust that it will be possible for sub sequent reviews under this title to pick up many of the important contribu tions which we have neglected. Inasmuch as the previous review of this area was devoted to reaction mechanisms, we have devoted much of our attention to the second of the chief directions of the field.

show abstract

“…Consequently, it was considered worthwhile to confirm one of them by a kinetic method. This method depends on the fact that the pseudo-first-order rate constant k+ for the hydrolysis of thionamides (38,39) (and also amides (40), thio-acids (4 I), thion-esters (42), and many other compounds) increases with acid concentration up to a maximum and then decreases (illustrated for thionacetamide in excess perchloric at 35°C (38) in Fig. 1).…”

Section: Results and Discussion P K I Values Of Diprotonated Cu-aminomentioning

confidence: 99%

“…5~hionacetamide was hydrolysed in aqueous perchloric acid (38), for which no HT scale has yet been determined. However, other acidity function scales almost coincide in perchloric and sulfuric acids of equal weight percent concentration (41), and we have assumed this to be true for HT also.…”

Section: Results and Discussion P K I Values Of Diprotonated Cu-aminomentioning

confidence: 99%

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Paventi¹,

Heirtzler²,

Edward³

1986

Can. J. Chem.

View full text Add to dashboard Cite

. 64,23 10 (1986). The first dissociation constants pK1 of four diprotonated cx-aminothionamides, determined spectrophotometrically, are between -8.1 to -8.8; the second dissociation constants pK2, of three of these compounds, determined titrimetrically, are between 7.3 and 7.7. Both pK1 and pK2 values are close to those calculated from current electrostatic theory for equilibria in solutions of zero ionic strength, in spite of the fact that data for pK1 values were obtained in solutions of high ionic strength. Results indicate a much larger effect of the charged ammonium group on the basicity of the thionamide group than on the basicity of the amide group. A possible explanation based on the greater hydration of the protonated amide group is advanced. MARTINO PAVENTI, FENTON HEIRTZLER et JOHN T. EDWARD. Can. J. Chem. 64, 2310Chem. 64, (1986. Utilisant des mCthodes spectrophotomCtriques on a determine les premieres constantes de dissociation (pK,) de quatre a-aminothioamides diprotones; comme Ctant entre -8,l et -8,8; faisant appel B des mCthodes titrimetriques, on a aussi determink les deuxikmes constantes de dissociation (pK2) de trois de ces composks comme etant entre 7,3 et 7,7. Les valeurs tant des pK1 que des pK2 sont proches des valeurs calculies a partir de la theorie ilectrostatique actuelle sur les Cquilibres dans des solutions de force ionique Cgale a zero, mCme si les donnees relatives aux valeurs de pKl sont obtenues dans des solutions de forces ioniques ClevCes. Les risultats indiquent que le groupement ammonium charge provoque un effet beaucoup plus important sur la basicit6 du groupement thionamide que sur la basicite du groupement amide. On propose une explication plausible qui est bas& sur une plus grande hydratation du groupement amide proton-6.[Traduit par la revue]Starting more than 60 years ago with Bjerruln ( I ) , a long succession of investigations has elaborated an electrostatic theory of substitutent effects which is gradually winning general acceptance (2-9). However, the electrostatic effect can be profoundly altered by the presence of a solvent, and although "emphasis has shifted from continuum electrostatics to interactions between specific functionalities in the ions and appropriate sites in a few solvent molecules" (lo), a discontinuous solvation model (1 1) of quantitative (as opposed to qualitative) predictive power has been slow to emerge.The older continuum solvent model was applied to electrostatic effects by Kirkwood and Westheimer (4) in 1938. As an example, we may consider the fact that the dissociation constant K2 of monoprotonated glycine 2 would be expected to be higher than KAH of the parent acid, acetic acid, because the substituted acetate ion 3 is stabilized by electrostatic interaction between NH3+ and the negatively charged carboxylate group.' On the other hand, further dissociation of 3 should be made more difficult than the dissociation of the parent methylammonium ion (KBH+) by the same electrostatic stabilization, the substituent now being C 0 2 -. Classic...

show abstract

A Study of the Mechanism and Kinetics of the Thioacetamide Hydrolysis Reaction¹

Cited by 63 publications

References 0 publications

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Physical Organic Chemistry

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Contact Info

Product

Resources

About

A Study of the Mechanism and Kinetics of the Thioacetamide Hydrolysis Reaction1

Cited by 63 publications

References 0 publications

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Ionization of Organic Compounds: V. Thiolactams in Sulphuric Acid

Physical Organic Chemistry

Basicity of the thionamide group of α-aminothionamides. Attenuation of electrostatic effects by solvation

Contact Info

Product

Resources

About

A Study of the Mechanism and Kinetics of the Thioacetamide Hydrolysis Reaction¹