Anhydrides reaction

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Fig. 2. Synthesis of uma2enil (18). The isonitrosoacetanihde is synthesized from 4-f1iioroani1ine. Cyclization using sulfuric acid is followed by oxidization using peracetic acid to the isatoic anhydride. Reaction of sarcosine in DMF and acetic acid leads to the benzodiazepine-2,5-dione. Deprotonation, phosphorylation, and subsequent reaction with diethyl malonate leads to the diester. After selective hydrolysis and decarboxylation the resulting monoester is nitrosated and catalyticaHy hydrogenated to the aminoester. Introduction of the final carbon atom is accompHshed by reaction of triethyl orthoformate to...

In the case of acids and acid anhydrides, reaction can also occur via the hydroxyl groups that are present, including those formed on opening of the epoxide ring. 

Phosphorus pentachloride, for conversion of pentaacetylgluconic add to add chloride, 41, 80 for oxidation of cycloheptatriene to tropylium fluoborate, 43, 101 with cyanoacetic acid, 41, 5 Phosphorus tribromide, reaction with 1.5-hexadien-3-ol, 41, 50 Phthalic anhydride, reaction with L-phenylalanine to yield N-phthalyl-L-phenylalanine, 40, 82 Phthalic monoperacid, 42, 77 N-Phthalyl-i.-alanine, 40, 84 N-Phthalyl-/3-alanine, 40, 84 N-Phthalylglycine, 40, 84 N-Phthalyl-l-/5-phenylalanine, 40, 82... 

Examples 9.1 and 9.2 used a distributed parameter model (simultaneous PDEs) for the phthalic anhydride reaction in a packed bed. Axial... 

Methanol-acetic anhydride reaction Fire Research Station Site Singh (1993)... 

Trimethylsilyl triflate is also a powerful catalyst for acylation by anhydrides. Reactions of alcohols with a modest excess (1.5 equival) of anhydride proceed in inert solvents at 0°C. Even tertiary alcohols react rapidly.114 The active acylation reagent is presumably generated by O-silylation of the anhydride. 

In a related study by the same authors, the effect of microwave irradiation on car-bodiimide-mediated esterifications on a solid support was investigated, employing benzoic acid [29]. The carboxylic acid was activated using N,N -diisopropylcarbodi-imide (DIC) through the O-acyl isourea or the symmetrical anhydride protocol (Scheme 7.9). The isourea protocol was carried out in a dichloromethane/N,N-di-methylformamide mixture in sealed vessels, whereas the anhydride reactions were carried out in l-methyl-2-pyrrolidinone (NMP) at atmospheric pressure. 

This route relies on 1,3-dipolar cycloaddition reactions a series of dihydropyrrolizines 213 were synthesized by heating the proline derivatives 211 with dimethyl acetylenedicarboxylate (DMAD) at 130-140 °C in the presence of acetic anhydride. Reaction between 211 and AczO provides the mesoionic oxazalone intermediate 212 which adds to dimethyl acetylenedicarboxylate, giving a cycloadduct, which undergoes spontaneous decarboxylation leading to 213 (Scheme 50) <1998JME4744, 1977JME812>. 

Up until the late 1980s, it was conventional wisdom that mixed-anhydride reactions should be carried out at low temperature under anhydrous conditions and not in... 

FIGURE 2.27 More on additives. In a carbodiimide-mediated reaction between acid 1 and amine 2, addition of HOObt can lead to the side reaction of aminolysis at the carbonyl of the activating moiety of ester 3, generating addition product 4. Addition of HOBt to a mixed-anhydride reaction containing unconsumed chloroformate generates mixed carbonate 5, leading to production of urethane 6. 

FIGURE 7.4 The mixed-anhydride reaction (see Section 2.6). Preparation of mixed anhydride 4 followed by its aminolysis (A) producing peptide 6 and the major side reaction of aminolysis at the wrong carbonyl (B) generating urethane 7. 

In fact, recent work indicates that less urethane is formed by aminolysis of an activated peptide than by aminolysis of an activated /V-al ko x y carbon y I am ino acid. Such results are consistent with the postulate that the intermediate undergoing aminolysis during the mixed anhydride reaction of a segment is the 2,4-dialkyl-5(4//)-oxazolonc, a tenet that is indicated by the high rate at which the activated peptide is converted to the oxazolone.10 13... 

KU Prasad, MA Iqbal, DW Urry. Utilization of 1-hydroxybenzotriazole in mixed anhydride reactions. Int J Pept Prot Res 25, 408, 1985. 

A second method of activating the acid for esterification (see Section 7.6) is as the mixed anhydride. The mixed-anhydride reaction had been employed decades ago for preparing activated esters. However, it was never adopted because of its unreliability and the modest yields obtained. The method was fine-tuned (Figure 7.12), after reliable information on the properties of mixed anhydrides was acquired (see Section 2.8). Tertiary amine is required for esterification of the mixed anhydride to occur. The method is generally applicable, except for derivatives of asparagine, glutamine, and serine with unprotected side chains. The base also prevents decomposition that occurs when the activated derivative is a Boc-amino acid (see... 

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