Temperature, acid hydrolysis

Wright, J. High-Temperature Acid Hydrolysis of Cellulose for Alcohol Fuel Production SERI/TR-231-1714 Solat Energy Research Institute Golden, CO, 1983. 

Yunus, R., Salleh, S. F., Abdullah, N., Biak, D. R. A. Effect of ultrasonic pre-treatment on low temperature acid hydrolysis of oil palm empty fruit bunch. Bioresource Technology 2010,101,9792-9796. 

Acylated Corticoids. The corticoid side-chain of (30) was converted iato the cycHc ortho ester (96) by reaction with a lower alkyl ortho ester RC(OR )2 iu benzene solution ia the presence of i ra-toluenesulfonic acid (88). Acid hydrolysis of the product at room temperature led to the formation of the 17-monoesters (97) ia nearly quantitative yield. The 17-monoesters (97) underwent acyl migration to the 21-monoesters (98) on careful heating with. In this way, prednisolone 17a,21-methylorthovalerate was converted quantitatively iato prednisolone 17-valerate, which is a very active antiinflammatory agent (89). The iatermediate ortho esters also are active. Thus, 17a,21-(l -methoxy)-pentyhdenedioxy-l,4-pregnadiene-liP-ol-3,20-dione [(96), R = CH3, R = C Hg] is at least 70 times more potent than prednisolone (89). The above conversions... 

Bromoacetic acid can be prepared by the bromination of acetic acid in the presence of acetic anhydride and a trace of pyridine (55), by the HeU-VoUiard-Zelinsky bromination cataly2ed by phosphoms, and by direct bromination of acetic acid at high temperatures or with hydrogen chloride as catalyst. Other methods of preparation include treatment of chloroacetic acid with hydrobromic acid at elevated temperatures (56), oxidation of ethylene bromide with Aiming nitric acid, hydrolysis of dibromovinyl ether, and air oxidation of bromoacetylene in ethanol. 

Hydrolysis in neutral aqueous solutions proceeds slowly at room temperature and more rapidly at acidic conditions and elevated temperatures. The hydrolysis—esterification reaction is reversible. Under alkaline conditions hydrolysis is rapid and irreversible. Heating the alkaline hydrolysis product at 200—250°C gives 4,4 -oxydibutyric acid [7423-25-8] after acidification (148). 

The extent of the initial hydrolysis depends on temperature and how the water is added. Hydrolysis is reduced at slower addition rates and lower temperatures. The hydrolysis subsequent to the initial fast reaction is slow, presumably because part of the acid is converted to fluorosulfate ions which hydrolyze slowly even at elevated temperatures. The hydrolysis in basic solution has also been studied (17). Under controlled conditions, hydrates of HSO F containing one, two, and four molecules of water have been observed (18,19). 

Acid Hydrolysis. With hot concentrated mineral acids, primary nitroparaffins yield a fatty acid and a hydroxylamine salt. If anhydrous acid and lower temperatures are used, the intermediate hydroxamic acid can be recovered. 

Both 5-hydroxyquiQoline [578-67-6] and S-hydroxyquiaoline [148-24-3] have been prepared ia good yields by the acid hydrolysis of the appropriate aminoquiaoline at temperatures of 180—235°C (124). The latter compound has been prepared ia several different ways, including sulfonation-fusion of quiaoline. Hydrolysis of 8-chloroquinoline [611-33-6] gives a 93% yield, whereas 80% is obtained ia a modified Skraup synthesis with o-aminophenol (125,126). 

The effects of both pH and temperature of aluminum alkoxide hydrolysis on gelation is shown in Eigure 8. Addition of acid into the mixture hydrolyzed at 90°C, and by consequence reduction of pH, reduces the gelation time of the samples, whereas in mixtures hydrolyzed at room temperature, acidic addition increases gelation time. 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Solutions of HEC are pseudoplastic. Newtonian rheology is approached by very dilute solutions as well as by lower molecular-weight products. Viscosities change Httie between pH 2 and 12, but are affected by acid hydrolysis or alkaline oxidation under pH and temperature extremes. Viscosities of HEC solutions change reversibly with temperature, increasing when cooled and decreasing when warmed. 

The influence of temperature, acidity and substituents on hydrolysis rate was investigated with simple alkyldiaziridines (62CB1759). The reaction follows first order kinetics. Rate constants and activation parameters are included in Table 2. 

M HCl at room temperature. Little, if any, use of these groups has been made by the general synthetic community, but the wide range of selectivities observed in their acidic hydrolysis should render them useful for the selective protection of poly functional molecules. 

Various combinations of Rf and R (equation 36) have been studied [39, 72, 73, 74, 75], and it appears that the stability of the lithium salt of the hemiketal is the major factor in determming the reaction products formed via paths A, B, or C in equation 37 Other important factors that affect the course of the reacbon are (1) thermal stability of the perfluoroalkyllithium compounds, (2) reaction temperature, (3) mode of addition of the reactants, (4) stenc hindrance, (5) nature of the Y group (in equation 36), and (6) temperature at which the reaction is terminated by acid hydrolysis... 

Arsine, AsHs, is formed when many As-containing compounds are reduced with nascent hydrogen and its decomposition on a heated glass surface to form a metallic mirror formed the basis of Marsh s test for the element. The low-temperature reduction of AsCls with LiAlH4 in diethyl ether solution gives good yields of the gas as does the dilute acid hydrolysis of many arsenides of electropositive elements (Na, Mg, Zn, etc.). Similar reactions yield stibine, e.g. ... 

The acid hydrolysis of diaziridines has been investigated kinetic-ally. The reaction is first order and shows a relatively high temperature coefficient. Thus one finds a relatively high activation enthalpy (23-28 kcal) and a positive activation entropy (2-6 eu). The influence of substitution on nitrogen is small. The velocity of the diaziridine hydrolysis depends only in the weakly acid region on the acid concentration. Between pH 7 and 3 the fc-values rise by nearly 10 . For the... 

Under appropriate conditions 1,3-dioxanes can be obtained in moderate to good yields. Below 70 °C the acid-catalyzed condensation of alkenes with aldehydes yields 1,3-dioxanes as major products, while at higher temperatures the hydrolysis of dioxanes to diols is observed. 

A further observation is the fact that differences in rates of nitration between the reagents prepared at different temperatures tended to zero as the water concentration of the added nitric acid was decreased to zero73. It has been argued that, since the acid-catalysed hydrolysis of acetic anhydride must be very rapid at 25 °C and removes water which initially competes with acetic anhydride and acetyl nitrate for protons, this removal permits equilibria (30) and (31) to be displaced towards products. The more anhydrous the nitric acid, the less important is this initial hydrolysis of the acetic anhydride and so the difference in the nitrating power of the differently prepared mixtures becomes less. When reagents are mixed at low temperatures, the hydrolysis of the anhydride is very slow, but once this is accomplished, formation of the protonated acetyl nitrate and subsequent nitration is rapid as observed73. 

Ethyl o-nitrophenylpyruvate and o-nitrophenylpyruvic acid 14-21 have been prepared by condensation of o-nitrotoluene with diethyl oxalate in the presence of potassium ethoxide,4 14 sodium ethoxide,16-20 or sodium methoxide.21 Sodium ethoxide is less reactive, however, and cannot be substituted successfully for potassium ethoxide in the present procedure, as it gives a very poor yield and poor quality of precipitated sodium salt. With sodium ethoxide the reaction does not appear to go to completion even under the conditions of refluxing ethanol usually employed,16-21 which are considerably more severe than the room temperature conditions employed with potassium ethoxide in the present procedure. o-Nitrophenylpyruvic add has also been prepared by hydrochloric acid hydrolysis of o-nitro-a-acetamino-dnnamic azlactone.4... 

A particular case of a [3C+2S] cycloaddition is that described by Sierra et al. related to the tail-to-tail dimerisation of alkynylcarbenes by reaction of these complexes with C8K (potassium graphite) at low temperature and further acid hydrolysis [69] (Scheme 24). In fact, this process should be considered as a [3C+2C] cycloaddition as two molecules of the carbene complex are involved in the reaction. Remarkable features of this reaction are (i) the formation of radical anion complexes by one-electron transfer from the potassium to the carbene complex, (ii) the tail-to-tail dimerisation to form a biscarbene anion intermediate and finally (iii) the protonation with a strong acid to produce the... 

---