Anhydrides symmetric

Acid Anhydrides. Symmetrical anhydrides of monocarboxylic acids, when unsubstituted, are named by replacing the word acid by anhydride. Anhydrides of substituted monocarboxylic acids, if symmetrically substituted, are named by prefixing bis- to the name of the acid and replacing the word acid by anhydride. Mixed anhydrides are named by giving in alphabetical order the first part of the names of the two acids followed by the word anhydride, e.g., acetic propionic anhydride or acetic propanoic anhydride. Cyclic anhydrides of polycarboxylic acids, although possessing a... 

Acid Anhydrides. Symmetrical anhydrides of monocarboxylic acids, when unsubsti-... 

The acylating reagent may be an acid chloride or an acid anhydride. Symmetrical ketones (—CH2 R = R2) yield only a single regioisomer. Thus acetone or cyclohexanone may be acylated with acetic anhydride in the presence of boron trifluoride-etherate to pentane-2,4-dione and 2-acetylcyclohexanone respectively (Expt 5.102). Both diketones are present in the reaction mixture as boron difluoride complexes [(10) and (11) respectively], from which they may be released by treatment with sodium acetate. Pentane-2,4-dione is appreciably water soluble and is isolated by means of its characteristic copper complex (12). 

In addition to the availability issues of the oxazolidinone unit, there has been some reluctance to scale up the reactions because formation of the V-acyl derivatives usually uses n-butyl lithium as a base. This problem can be circumvented by the use of an acid chloride or anhydride (symmetric or mixed) with triethylamine as the base in the presence of a catalytic amount of DMAP (4-dimethylamino pyridine). The reaction is general and provides good yields even with a,P-unsatur-ated acid derivatives (Scheme 2.4).12... 

In peptide chemistry, in addition to the initially used acid chloride methodb h A -Phth amino acids can be coupled by the entire repertoire of coupling methods, i.e. mixed anhydrides, symmetrical anhydride, active ester, and the azide method.W Due to the add stability of A -phthaloyl derivatives, the acid hydrolyses of esters are readily performed.b h... 

If the two carboxylic acid molecules forming the acid anhydride are the same, the anhydride is a symmetrical anhydride. If the two carboxylic acid molecules are different, the anhydride is a mixed anhydride. Symmetrical anhydrides are named by using the acid name and replacing acid with anhydride. Mixed anhydrides are named by stating the names of both acids in alphabetical order, followed by anhydride. ... 

Anhydrides. - Symmetrical acyclic anhydrides can be easily obtained from the corresponding carboxylic acids in 59-80% yields... 

Formation of Symmetrical Anhydrides. Symmetrical carboxylic anhydrides are useful reagents for peptide or amide synthesis. Unfortunately, most methods require transformation of the acid first into the acid chloride or the use of condensation agents, e.g. 1,3-Dicyclohexylcarbodiimide (DCC), which can lead to separation problems of the product anhydride from the hydrated derivatives of the condensation reagents. The use of Thionyl Chlo-ridelPyridine to form the acid chloride is often complicated by racemization with amino acid derivatives. 

Anilino vinyl derivatives of thiazolium (30, R = H) or acetanilido (30, R = C0CH3), as well as formyl methylene 30b (methods E-G), give asymmetrical dyes when condensed with a methyl reactive group of another species (Scheme 42). Mesosubstituted symmetrical or unsymmet-rical thiazolocyanines are obtainable via /S-alkylmercaptovinyl thiazolium derivatives (32) (methods H and I) (Scheme 43). a or /S carbon atoms of the trimethine chain can be substituted by acetyl when a dye is treated with acetic anhydride (method L). The hydrolysis of neocyanines lead to trimethine cyanine by fractional elimination of a composant chain (method K). 

This procedure is applicable to the preparation of both symmetrical anhydrides (R and R the same) and mixed anhydrides (R and R different)... 

Infrared IR spectroscopy is quite useful in identifying carboxylic acid derivatives The, carbonyl stretching vibration is very strong and its position is sensitive to the nature of IKT the carbonyl group In general electron donation from the substituent decreases the double bond character of the bond between carbon and oxygen and decreases the stretch mg frequency Two distinct absorptions are observed for the symmetric and antisym metric stretching vibrations of the anhydride function... 

First prepared by C. F. Gerhardt from ben2oyl chloride and carefully dried potassium acetate (1), acetic anhydride is a symmetrical iatermolecular anhydride of acetic acid the iatramolecular anhydride is ketene [463-51-4]. Benzoic acetic anhydride [2819-08-1] undergoes exchange upon distillation to yield benzoic anhydride [93-97-0] and acetic anhydride. 

Synthesis. Symmetrical diacyl peroxides (20, R = R = alkyl or aryl) are prepared by the reaction of an acyl chloride or anhydride with sodium peroxide or hydrogen peroxide and a base ... 

Anhydride Formation. The carboxyl group ia A/-protected amino acids is converted iato the symmetrical anhydride on treatment with the carbodiimide (84). 

The symmetrical diesters are produced by esterification of maleic anhydride, followed by addition of sodium bisulfite across the double bond (see... 

The reaction is not suitable for hindered carboxylic acids, since considerable symmetrical anhydride formation (52% with pivalic acid) results. Symmetrical anhydride formation can sometimes be suppressed by the use of stoichiometric quantities of DMAP. 

In the case of very hindered acids the yields are poor and formation of the symmetrical anhydride is observed. Useful selectivity can be achieved for a less hindered acid in the presence of a more hindered one. ... 

The symmetrical dialkyl succinic acids exist in tw o forms, each yielding a separate anhydride. From their similaritv to... 

Symmetrical anhydrides of unsubslituted monocarboxylic acids and cyclic anhydrides of dicarboxylic acids are named by replacing the word acid with anhydride. 

Conversion of Acid Halides into Anhydrides Nucleophilic acyl substitution reaction of an acid chloride with a carboxylate anion gives an acid anhydride. Both symmetrical and unsymmetrical acid anhydrides can be prepared in this way. 

Fig. 6 Microwave-assisted loading protocol of symmetric anhydrides to hydroxymethyl PS...

Unsymmetrical as well as symmetrical anhydrides are often prepared by the treatment of an acyl halide with a carboxylic acid salt. The compound C0CI2 has been used as a catalyst. If a metallic salt is used, Na , K , or Ag are the most common cations, but more often pyridine or another tertiary amine is added to the free acid and the salt thus formed is treated with the acyl halide. Mixed formic anhydrides are prepared from sodium formate and an aryl halide, by use of a solid-phase copolymer of pyridine-l-oxide. Symmetrical anhydrides can be prepared by reaction of the acyl halide with aqueous NaOH or NaHCOa under phase-transfer conditions, or with sodium bicarbonate with ultrasound. 

If the reaction of the 2,3-disubstituted-l, 3-butadienes is with a symmetric dienophile, such as maleic anhydride, the 2 and 3 positions in the diene are equivalent, and therefore... 

Opening the anhydride and writing the enol as a ketone reveals that we are trying to make an a-ketoacld (51), The best disconnection Is (51a) which uses the 1.3-dlcarbonyl relationship, Is next to a branchpoint, and produces a symmetrical starting material (52), Ana lysis... 

The lactone ring in (9) is now a serious problem. If it were a symmetrical ring - say an anhydride (10) -we could make it easily by a 2 + 2 cycloaddition, as it would be symmetrical. 

From a commercial viewpoint the most important compounds of this class are the 3,3-(bisindol-3-yl)phthalides. The first synthesis47 involved Route B as described in Scheme 7, in which a second indole derivative condenses with the indolylbenzoylbenzoic acid in acetic anhydride. However, for the preparation of symmetrical derivatives it has been shown61 that a one-pot process, avoiding isolation of the intermediate and use of aluminum chloride, is more convenient. 

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