Mechanisms of bromination of uracil derivatives. 4. Formation of adducts in acidic aqueous solutions and their dehydration to 5-bromouracils

1979 ◽  
Vol 57 (6) ◽  
pp. 626-634 ◽  
Author(s):  
Oswald S. Tee ◽  
Sujit Banerjee
Keyword(s):  
Sulfuric Acid ◽  
Aqueous Solutions ◽  
Isotope Effects ◽  
Uracil Derivatives ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The reactions of bromine with uracil, 1-methyluracil, 3-methyluracil, and with 1,3-dimethyluracil in 0.125–2.0 M aqueous sulfuric acid have been examined. Under these conditions rapid attack by bromine upon the uracil leads to the formation of an observable intermediate, a 5-bromo-5,6-dihydro-6-hydroxyuracil, which subsequently undergoes slow acid-catalyzed dehydration to the appropriate 5-bromouracil. The intermediates derived from uracil and 3-methyluracil also show acid independent dehydration. The dehydration of the adduct derived from 6-methyluracil proceeds much more rapidly and so precludes observation of that adduct. The dehydrations show significant primary isotope effects for the rupture of C(5)—H bonds of the intermediates. The mechanistic implications of these results are discussed.

The decomposition of aliphatic N-nitro amines in aqueous sulfuric acid. Bisulfate as a nucleophile

1996 ◽  
Vol 74 (10) ◽  
pp. 1774-1778 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Rate Constants ◽  
Activation Parameters ◽  
Standard State ◽  
Aqueous Sulfuric Acid ◽  
Alkyl Groups ◽  
Different Temperatures ◽  
State Rate ◽  
Acid Catalyzed

In aqueous sulfuric acid, aliphatic N-nitro amines decompose to N2O and alcohols. An excess acidity analysis of the observed rate constants for the reaction shows that free carbocations are not formed. The reaction is an acid-catalyzed SN2 displacement from the protonated aci-nitro tautomer, the nucleophile being a water molecule at acidities below 82–85% H2SO4, and a bisulfate ion at higher acidities. Bisulfate is the poorer nucleophile by a factor of about 1000. Twelve compounds were studied, of which results obtained for nine at several different temperatures enabled calculation of activation parameters for both nucleophiles. The reaction appears to be mainly enthalpy controlled. The intercept standard-state rate constants are well correlated by the σ* values for the alkyl groups; the slopes are negative, with a more negative value for the slower bisulfate reaction. Interestingly the m≠m* slopes also correlate with σ*, although the scatter is bad. Key words: N-nitro amines, excess acidity, bisulfate, nucleophiles, acid-catalyzed, kinetics.

ChemInform Abstract: Hydroxylamine Production via Hydrogenation of Nitric Oxide in Aqueous Sulfuric Acid Catalyzed by Carbon-Supported Platinum.

ChemInform ◽  
1987 ◽  
Vol 18 (51) ◽  
Author(s):  
S. POLIZZI ◽  
A. BENEDETTI ◽  
G. FAGHERAZZI ◽  
C. GOATIN ◽  
R. STROZZI ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Sulfuric Acid ◽  
Aqueous Sulfuric Acid ◽  
Supported Platinum ◽  
Acid Catalyzed

THE WALLACH REARRANGEMENT: PART II. KINETICS AND MECHANISM OF THE ACID-CATALYZED REARRANGEMENT OF AZOXYBENZENE

1965 ◽  
Vol 43 (4) ◽  
pp. 862-875 ◽  
Author(s):  
E. Buncel ◽  
B. T. Lawton
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Acid Concentration ◽  
Entire Range ◽  
Kinetics And Mechanism ◽  
The Other ◽  
Rate Data ◽  
Spectrophotometric Methods ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3–96.4% sulfuric acid at 25° and in 65.0–90.4% sulfuric acid at 75.5° by spectrophotometric methods. The pKa of azoxybenzene in aqueous sulfuric acid has also been determined. It is found that although azoxybesssnzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1 000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (II) as the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.

The Meyer Reaction of Phenylnitromethane in Acid. I. The Reactions of Phenyl-aci-nitromethane in Acid

1971 ◽  
Vol 49 (21) ◽  
pp. 3483-3488 ◽  
Author(s):  
J. T. Edward ◽  
P. H. Tremaine
Keyword(s):  
Sulfuric Acid ◽  
Room Temperature ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Benzohydroxamic Acid ◽  
Aqueous Sulfuric Acid

Phenyl-aci-nitromethane reacts in aqueous sulfuric acid at room temperature to form phenylnitromethane and benzohydroxamic acid. The relative amounts of these two products depend on the concentration of the acid. Benzohydroxamic acid is formed by reaction of the intermediate, benzonitrile oxide, with water.Solvent effects, substituent effects, and isotope effects have been studied to determine mechanisms for these reactions of phenyl-aci-nitromethane.

The Mechanism of Bromination of 2(1H)-Pyrimidinone, its N-Methyl and N,N′-Dimethyl Derivatives in Aqueous Acidic Solution

1974 ◽  
Vol 52 (3) ◽  
pp. 451-457 ◽  
Author(s):  
Oswald S. Tee ◽  
Sujit Banerjee
Keyword(s):  
Sulfuric Acid ◽  
Acidic Solution ◽  
Acid Solutions ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed ◽  
Aqueous Acidic Solution ◽  
Sulfuric Acid Solutions

Rates of bromination at the 5-positions of the title compounds have been measured in aqueous sulfuric acid solutions. The reaction involves a rapid irreversible formation of a 5-bromo-4,6-dihydroxy-hexahydro-2-oxopyrimidine which undergoes slow acid-catalyzed conversion to the corresponding 5-bromopyrimidinone. If excess bromine is present the latter product reacts further to produce a 5,5-dibromo-4,6-dihydroxyhexahydropyrimidine.

Mechanistic variation in the reactions of substituted acetamides in aqueous sulfuric acid

1984 ◽  
Vol 62 (11) ◽  
pp. 2401-2414 ◽  
Author(s):  
Linda M. Druet ◽  
Keith Yates
Keyword(s):  
Sulfuric Acid ◽  
Water Molecules ◽  
Acid Solutions ◽  
Reaction Products ◽  
Aqueous Sulfuric Acid ◽  
Rate Determining Step ◽  
Wide Range ◽  
Acid Catalyzed ◽  
Catalyzed Reactions ◽  
Sulfuric Acid Solutions

The acid-catalyzed reactions of acetamide 1, N-tert-butylacetamide 2, and several p-substituted N-benzylacetamides (3 = H, 4 = CH3, 5 = OCH3, 6 = Cl, 7 = NO2) have been studied as a function of acidity and temperature over a wide range of aqueous sulfuric acid solutions (0–91%). Analysis of the reaction products and rate–acidity profiles revealed that four different mechanisms are operative over different acidity regions depending on the structure of the substrate. These are: two A-2 hydrolysis mechanisms with N-acyl fission of the substrate (with participation of one or several water molecules in the rate-determining step); A-1 hydrolysis with N-alkyl fission; and sulfonation, followed by hydrolysis. These conclusions are supported by three complementary and detailed kinetic treatments based on the hydration parameter, transition state activity coefficient, and excess acidity approaches. The acidity domains of each mechanism have been established for each substrate. The mechanistic conclusions are fully supported by the different values of ΔH‡ and ΔS‡ obtained in different regions of acidity.

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