Hydrolysis of Some Poly(ortho-ester)s in Homogeneous Solutions

1984 ◽  
Vol 73 (11) ◽  
pp. 1563-1568 ◽  
Author(s):  
Tue Huu Nguyen ◽  
Chung Shih ◽  
Kenneth J. Himmelstein ◽  
Takeru Higuchi
Keyword(s):  
Ortho Ester ◽  
Homogeneous Solutions ◽  
Hydrolysis Of

Hydrolysis of trioxaadamantane ortho esters. I. Dialkoxycarbocation – ortho ester equilibrium and acidity function

1984 ◽  
Vol 62 (6) ◽  
pp. 1068-1073 ◽  
Author(s):  
Robert A. McClelland ◽  
Patrick W. K. Lam
Keyword(s):  
Acid Concentration ◽  
Intramolecular Interaction ◽  
Uv Spectroscopy ◽  
Equilibrium Constants ◽  
Hydrolysis Product ◽  
Acidity Function ◽  
Ortho Ester ◽  
Aromatic Substituent ◽  
Ortho Esters ◽  
Hydrolysis Of

3-Aryl-2,4,10-trioxaadamantane ortho esters (T) undergo a rapid equilibration with a ring-opened dioxan-2-ylium ion (DH+) prior to hydrolysis to product (a 1,3,5-cyclohexanetriol monobenzoate). The cation is stable in concentrated H2SO4 solutions where it has been characterized by nmr spectroscopy. It is observed using uv spectroscopy in dilute acids, and the ratio [DH+]/[T] at equilibrium has been measured as a function of acidity. Reversibility of the ring opening is established by the pattern of plots of cation absorbance versus acid concentration and by the observation that solutions containing cation on neutralization or dilution yield ortho ester, not hydrolysis product. Equilibrium constants for the reaction [Formula: see text] have been measured by obtaining the acidity function HT for this system. The effects of the aromatic substituent and the steepness of the acidity function plot versus acid concentration are interpreted in terms of a strong intramolecular interaction in the cation between the cationic center and the hydroxyl oxygen.

Enolic Ortho Esters. I. Preparation and Birch Reduction of Some Coumarinoid Ortho Esters

1989 ◽  
Vol 42 (8) ◽  
pp. 1235 ◽  
Author(s):  
DJ Collins ◽  
LM Downes ◽  
AG Jhingran ◽  
SB Rutschmann ◽  
GJ Sharp
Keyword(s):  
Carbon Tetrachloride ◽  
Acid Hydrolysis ◽  
Boron Trifluoride ◽  
Boron Trifluoride Etherate ◽  
High Yield ◽  
Ortho Ester ◽  
Birch Reduction ◽  
High Yields ◽  
Ortho Esters ◽  
Hydrolysis Of

Phenolic ortho esters such as 4′,4′-dimethylspiro[2H-1-benzopyran-2,2′-[1,3]dioxolan] (7b) and 4′,4′-dimethyl-3,4-dihydrospiro[2H-1-benzopyran-2,2′-[1,3]dioxolan] (9c) were prepared in low yields by reaction of 2H-1-benzopyran-2-one (5) or 3,4-dihydro-2H-1-benzopyran-2-one (8a) with 2,2-dimethyloxiran in carbon tetrachloride in the presence of boron trifluoride etherate. 3,4-Dihydrospiro[2H-1-benzopyran-2,2′-[1,3] dioxoan ] (9a) and the corresponding 7-methoxy compound (9e) were obtained in high yield by reaction of (8a) or its 7-methoxy analogue (8b) with 1,2-bis(trimethylsily1oxy)ethane (10) in the presence of trimethylsilyl trifluoromethane-sulfonate . Birch reduction of phenolic ortho esters such as (9c) and (9e) afforded the enolic ortho esters 4′,4′-dimethyl-3,4,5,8-tetrahydrospiro[2H-1-benzopyran-2,2′-[1,3] dioxola n] (11a) and 7-methoxy-3,4,5,8-tetrahydrospiro[2H-1-benzopyran-2,2′-[1,3]dioxolan] (llc) in high yields. Birch reduction of 4′,4′,5′,5′-tetramethylspiro[2H-1-benzopyran-2,2′-[1,3]dioxolan] (7c) gave a 1 : 3 mixture of 4′,4′,5′,5′-tetramethyl-3,4-dihydrospiro[2H-1-benzopyran-2,2′-[l,3] dioxolan ] (9d) and the corresponding 3,4,5,8-tetrahydro compound (11b). Acid hydrolysis of the enolic ortho ester (11a) gave 67% of 2-hydroxy-2-methylpropyl 3-(2-oxocyclohex-3-enyl) propanoate (20).

scholarly journals THE INFLUENCE OF THE SUBSTRATE CONCENTRATION ON THE RATE OF HYDROLYSIS OF PROTEINS BY PEPSIN

1920 ◽  
Vol 2 (6) ◽  
pp. 595-611 ◽  
Author(s):  
John H. Northrop
Keyword(s):  
Relative Rate ◽  
Total Concentration ◽  
Mass Action ◽  
Protein Solutions ◽  
Law Of Mass Action ◽  
Active Mass ◽  
Homogeneous Solutions ◽  
Rate Of Hydrolysis ◽  
The Law ◽  
Hydrolysis Of

1. It is pointed out that the apparent exceptions to the law of mass action found in enzyme reactions may be found in catalytic reactions in strictly homogeneous solutions. 2. These deviations in the rate of reaction from the law of mass action may be explained by the hypothesis that the active mass of the reacting substances is not directly proportional to the total concentration of substance taken. 3. In support of this suggestion it is shown that for any given concentration of pepsin the relative rate of digestion of concentrated and of dilute protein solutions is always the same. If the rate of digestion depended on the saturation of the surface of the enzyme by substrate the relative rate of digestion of concentrated protein solutions should increase more rapidly with the concentration of enzyme than that of dilute solutions. This was found not to be true, even when the enzyme could not be considered saturated in the dilute protein solutions. 4. The rate of digestion and the conductivity of egg albumin solutions of different concentration were found to be approximately proportional at the same pH. This agrees with the hypothesis first expressed by Pauli that the ionized protein is largely or entirely the form which is attacked by the enzyme. 5. The rate of digestion is diminished by a very large increase in the viscosity of the protein solution. This effect is probably a mechanical one due to the retardation of the diffusion of the enzyme.

Toward Tertiary Amine-Modulated Acid-Triggered Hydrolysis of Copolymers Containing Pendent Ortho Ester Groups

2013 ◽  
Vol 46 (3) ◽  
pp. 1093-1100 ◽  
Author(s):  
Cheng-Cheng Song ◽  
Cui-Cui Su ◽  
Jing Cheng ◽  
Fu-Sheng Du ◽  
De-Hai Liang ◽  
...  
Keyword(s):  
Tertiary Amine ◽  
Ortho Ester ◽  
Hydrolysis Of

scholarly journals Hydrolysis of Disaccharides by Metal Species in Neutral Homogeneous Solutions

2009 ◽  
Vol 38 (7) ◽  
pp. 728-729 ◽  
Author(s):  
Daisuke Takahashi ◽  
Sakiko Kobayashi ◽  
Kana Tsumura ◽  
Kazunobu Toshima
Keyword(s):  
Metal Species ◽  
Homogeneous Solutions ◽  
Hydrolysis Of

Precipitation of Iron(III) Hydroxides from Homogeneous Solutions

1996 ◽  
Vol 432 ◽  
Author(s):  
Yiwei Deng
Keyword(s):  
Natural Waters ◽  
Ferric Ions ◽  
Homogeneous Solutions ◽  
Size And Shape ◽  
Conventional Procedure ◽  
Rapid Hydrolysis ◽  
Redox Boundary ◽  
Hydrolysis Of

AbstractThe technique of precipitation from homogeneous solutions was used in this study to simulate the formation of iron(III) hydroxides under conditions similar to those at the redox boundary in natural waters. The technique allowed the precipitation of iron(III) hydroxides to occur when the precipitant iron(III) was slowly generated by the oxygenation of iron(II) and subsequently hydrolyzed. During the precipitation, no pH heterogeneity occurred locally as it was usually observed in the conventional preparation of iron(III) hydroxides in the laboratory. Thus, the rapid hydrolysis of ferric ions and the subsequent polymerization of iron(III) hydroxides were effectively prevented. The iron(III) precipitates formed in this way are more representative of the iron(III) particles occurring at the redox boundary in natural waters than those formed by the conventional procedure in the laboratory. The effect of solutes (e.g., H4SiO4) on the structure, size and shape of the iron(llI) hydroxides formed has also be studied.

Hydrolysis of trioxaadamantane ortho esters. II. Kinetic analysis and the nature of the rate-determining step

1984 ◽  
Vol 62 (6) ◽  
pp. 1074-1080 ◽  
Author(s):  
Robert A. McClelland ◽  
Patrick W. K. Lam
Keyword(s):  
Rate Constants ◽  
Product Formation ◽  
Low Ph ◽  
Acid Solutions ◽  
Ortho Ester ◽  
Rate Determining Step ◽  
Acid Catalyzed ◽  
Cation Hydration ◽  
Ortho Esters ◽  
Hydrolysis Of

A detailed kinetic study of the hydrolysis of a series of 3-aryl-2,4,10-trioxaadamantanes is reported. These ortho esters equilibrate with the ring-opened dialkoxycarbocation, in a very rapid process which could be studied using temperature-jump spectroscopy for aryl = 2,4-dimethylphenyl. Relaxation rate constants are of the order of 104 s−1; these could be analyzed to provide the rate constants for both the ring opening and the ring closing. Product formation from this equilibrating mixture is much slower. In acid solutions (0.01 M H+ −50% H2SO4), first-order rate constants for product formation initially increase with increasing acidity, but a maximum is reached at 20–35% H2SO4 and the rate then falls. This behavior is explained by a counterbalancing of two factors. Increasing acidity increases the amount of the dialkoxycarbocation in the initial equilibrium, but, outside the pH region, it decreases the rate of hydrolysis of this cation through a medium effect. Rate constants over a range of pH have been measured for two trioxaadamantanes and for the cation DEt+ derived by treatment of the ortho ester with triethyloxonium tetraafluoroborate. The latter models the cation formed in the ortho ester hydrolysis but it cannot ring close. Rate–pH profiles obtained in these systems are more complex than expected on the basis of rate-determining cation hydration. An interpretation is proposed with a change in rate-determining step between high pH and low pH. Cation hydration is rate determining at high pH but at low pH hemiorthoester decomposition becomes rate determining. Under these conditions the hemiorthoester equilibrates with both the dialkoxycarbocation and with the trioxaadamantane. The change in rate-determining step occurs because acid-catalyzed reversion of the hemiorthoester to dialkoxycarbocation is a faster process than acid-catalyzed hemiorthoester decomposition. This makes the latter rate-determining in acid solutions. Additional pathways available to the decomposition, however, make it the faster process at higher pH. A kinetic analysis furnishes all of the rate and equilibrium constants for the system, and provides support for the mechanistic interpretation. A comparison of these numbers with those obtained for the three stages in the hydrolysis of a simple monocyclic ortho ester underlines the novelty of the trioxaadamantane system.

Transformations of steroidal neopentyl systems. II. Migration of acetate from the 3β- to the 19-hydroxyl in Δ5 and A/B-trans steroids

1967 ◽  
Vol 45 (7) ◽  
pp. 707-711 ◽  
Author(s):  
J. Wicha ◽  
E. Caspi
Keyword(s):  
Ortho Ester ◽  
Reaction Proceeds ◽  
Ether Oxygen ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Intramolecular Mechanism

Acid-catalyzed hydrolysis of 19-triphenylmethyloxy-3β-acetoxy-Δ5 and -A/B-trans steroids gave the corresponding 19-acetoxy-3β-hydroxy products. In the absence of the 19-triphenylmethyloxy group, transesterification did not occur. Evidence supporting an intramolecular mechanism is presented. It is suggested that the reaction proceeds via an ortho ester VII resulting from the attack of the 19-ether oxygen on the "acetate cation" VI formed by the protonation of the acetate carbonyl.

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