Application Of The H<sub>0</sub> Acidity Function To Kinetics And Mechanisms Of Acid Catalysis

Long, F. A.; Paul, Martin A.

doi:10.1021/cr50017a003

Cited by 201 publications

(57 citation statements)

References 149 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…by the volume of activation of step [2]. If [2a] is the slow step then the transition state is bigger than the reactants and the volume of activation is positive or close to zero; this occurs in the acid-catalyzed hydrolysis of sucrose (4), dimethoxy~nethane, cliethoxymethane, dimethoxyethane, ancl triethoxymethane ( 5 ) .…”

Section: Discussionmentioning

confidence: 99%

“…If the Zucker-Hammett hypothesis (10,2), that when rates in concentrated acids are proportional to Hammett's acidity function lzo the mechanisn~ is A-1 and when rates are proportional to concentration of hydrogen ion the mechanism is A-2, is correct then the rate of hydrolysis of diethyl ether should be proportional to concentration of strong acicl. Values of Ilo ( = -log ho) are not ltnown for perchloric acid in water a t the temperature and pressure of the measurements, 120.1°C and 50 atm.…”

Section: Discussionmentioning

confidence: 99%

“…There is no firm evidence about which mechanism is followed, though Long and Paul (2) have noted that the entropies of activatioil calculated from the measurements of Skrabal and Zahorka (3) are positive and say that this suggests that the mechanism for primary and secondary ethers is A-1. I t was shown in Part I of this series of papers (4) that there are no grounds for thinking that entropies of activation of A-2 reactions cannot be positive, and consequently, the coilclusion of Long and Paul is not valid.…”

Section: I121mentioning

confidence: 99%

See 2 more Smart Citations

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Koskikallio¹,

Whalley²

1959

Can. J. Chem.

View full text Add to dashboard Cite

The acid-catalyzed hydrolysis of diethyl ether has been ~neasured in the te~nperature range 120-160" C a t low acid concentrations; the entropy of activation is -9 . 0 f -2.5 cal deg-1 mole-'. The effect of pressures up t o 3000 atm has been measured a t 161.2O C ; the volume of activation a t 1 atm is -8 . 5 f -2 cm3 mole-'. These two results show that the slow step is bi~nolecular. The rate in concentrated acids was measured a t l l g O C ; the rate was ~n u c h more nearly proportional to the acidity function ko than t o concentration of acid. This is contrary to the predictions of the Zucker-Hammett hypothesis, which is therefore not valid for the hydrolysis of diethyl ether. INTRODUCTIONDiethyl ether hydrolyzes to ethanol by acid catalysis (see ref. 1 for review). The reaction is presumed to involve a pre-equilibrium proton-transfer to the ether though there is no compelling evidence for this. Two possible slow steps are the unimolecular decomposition of the conjugate acid (A-1 mechanism)or its bimolecular substitution (A-2 mechanism)There is no firm evidence about which mechanism is followed, though Long and Paul (2) have noted that the entropies of activatioil calculated from the measurements of Skrabal and Zahorka (3) are positive and say that this suggests that the mechanism for primary and secondary ethers is A-1. I t was shown in Part I of this series of papers (4) that there are no grounds for thinking that entropies of activation of A-2 reactions cannot be positive, and consequently, the coilclusion of Long and Paul is not valid.I t has been shown (4, 5 , 6) that the A-1 and A-2 mechanisms can be distinguished by measuring reaction rates under pressure, and in this paper the technique is applied to the hydrolysis of diethyl ether. The measurements of Skrabal and Zahorka (3) of the hydrolysis of diethyl ether catalyzed by 0.5-il.1 p-toluenesulphonic acid indicate a rapid variation with temperature of the Arrhenius energy and of the entropy of activation, and rates over a temperature range have been measured in an attempt to verify this. Measurements of the rates over a range of acid concentrations have been made in order t o examine the validity of the Zucker-Hammett hypothesis. E X P E R I M E N T A L METHODSBecause the rates of hydrolysis are slow it is necessary to measure them a t fairly high temperatures, and the range 120-160' C has been used. Because ether is very volatile and not very soluble in water it is most important to avoid having a vaporspace above the reaction mixture in order to avoicl loss of reactant from the solution. Consequently, all reported rate measurements were clone in such a way that there was no

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: I121mentioning

confidence: 99%

See 1 more Smart Citation

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Koskikallio¹,

Whalley²

1959

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…The Zucker-Hammett hypothesis (7,8) is -0.57 (Table IV, (Table I ) , all in hydrochloric acid solutions. Thus the expected relationship is realized.…”

Section: -mentioning

confidence: 97%

“…Later, such reactions were considered to fall into two categories in which slopes were unity in plots of log k$ against either -Ho or log [H+] (7,8). Since the abandonment of these hypotheses, two systems have been employed to characterize the medium effect on reaction rate.…”

Section: Cowiparison With Correlations Of Other Typesmentioning

confidence: 99%

Linear Free Energy Relationships Concerning Reaction Rates in Moderately Concentrated Mineral Acids

Bunnett¹,

Olsen²

1966

Can. J. Chem.

View full text Add to dashboard Cite

ABSTR.-\CT Linear relationships exist between log k~ + I I o (for reactions of weakly basic substrates) or log k+ (for reactions of strongly basic substrates) and (Ho + log [Hf]). These are linear free energy relationships. For weakly basic sttbstrates, the correlations obtained are better than in plots of (log k+ + Ho) versus log an20 or of log k+ versus -Ha. The slopes in plots of log k+ or (log k+ + Ho), as appropriate, against (Ho + log [H+]) are taken a s parameter, 4, which characterizes the response of the reaction rate to changing rninera! acid col~centration. Values of 4 for reactions of strongly basic substrates reflect only relationships between protonated s~~b s t r a t e and transition state, and Inay be related to reaction mechanism. 4 values for reactions of weakly basic substrates reflect both equilibri~l~n protonation of the substrate and transformation of protonated substrate to transition state, and are therefore less directly related to ~nechanisin. However, the 4 values for the two steps are additive and that for the latter step can be obtained by subtraction if the overall 4 value and that for equilibrium protonation are known.The rates and states of equilibrium of reactions in moderately concentrated mineral acid solutions generally vary with the acid concentration. The extent and even the direction of variation differ from reaction to reaction. The description, quantification, and interpretation of these phenomena have occupied the attention of inany ivorlters, but understanding renlains illcomplete.In the accoinpanying paper (I) it is shown that linear free energy relatioilships (1.f.e.r.) exist between the logarithills of equilibrium quotients, [SI-If]/ [S] [Hf], and (or) secondorder rate coefficients for diverse reactions as these quantities vary lvith acid concentration. These relationships as they pertain to equilibria are considered in that paper. They are now considered as they pertain t o rate phenomena.T h a t 1.f.e.r. concerning kinetic data exist is illustrated by Fig. 1 of the accoinpanying paper and by Figs. 1 and 2 of this one. In the present Fig. 1, the logarithm of the secondorder rate coefficient (k+/[I-If], alternatively syinbolized kz) for the enolization of acetophenone (data of Zucker and I-Tainmett (2)) in perchloric acid solutions is plotted against log kz for the depolyinerization of trioxane (interpolated from data of Bell, Bascombe, and McCoubrey (3)) in perchloric acid solutions. Each point represents measurements a t a different acid concentration, points for lower acid concentrations being to~vard the left of the plot. In Fig. 2, log kz for ethyl acetate hydrolysis (interpolated froin data of Bell, Dowding, and Noble (4)) is plotted against log k+ for hydrolysis of N,N1-diphenylformamidine (data of DeFVolfe ( 5 ) ) , both in hydrochloric acid solutions. The latter substrate is strongly basic, essentially fully protonated a t all the acid concentrations studied, and one therefore plots log kJ, rather than log kz.For purposes of formulating 1.f.e.r. concerning e...

show abstract

Solvent effects on reactions of hydroxide ion with phosphorus(V) esters. A quantitative treatment

Bunton

Gillitt

Kumar

1996

J. Phys. Org. Chem.

View full text Add to dashboard Cite

Second‐order rate constants of reactions of HO− with phosphate, phosphinate and thiophosphinate esters, (PhO)2PO.OC6H4NO2‐p, Ph2PO.OC6H4NO2‐p, Ph2PO.SPh, Ph2PO.SC6H4NO2‐p and Ph2PO.SEt, go through minima with decreasing water content of H2O‐MeCN or H2O‐t‐BuOH. The rate decrease is due to stabilization of the non‐ionic ester on addition of organic solvent to H2O. This inhibition is partially offset by stabilization of the anionic transition states and in the drier solvents partial desolvation of HO− increases rates.

show abstract

Application Of The H₀ Acidity Function To Kinetics And Mechanisms Of Acid Catalysis

Cited by 201 publications

References 149 publications

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Linear Free Energy Relationships Concerning Reaction Rates in Moderately Concentrated Mineral Acids

Solvent effects on reactions of hydroxide ion with phosphorus(V) esters. A quantitative treatment

Contact Info

Product

Resources

About

Application Of The H0 Acidity Function To Kinetics And Mechanisms Of Acid Catalysis

Cited by 201 publications

References 149 publications

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Pressure Effect and Mechanism in Acid Catalysis: Iv. The Hydrolysis of Diethyl Ether

Linear Free Energy Relationships Concerning Reaction Rates in Moderately Concentrated Mineral Acids

Solvent effects on reactions of hydroxide ion with phosphorus(V) esters. A quantitative treatment

Contact Info

Product

Resources

About

Application Of The H₀ Acidity Function To Kinetics And Mechanisms Of Acid Catalysis