Acid 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). 

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. 

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. 

Achiral, C -symmetric unbridged metallocenes, 16 104 Achiral hydrobora ting agents, 13 667 Achiral molecules, 6 73 Acicular reinforcement, 5 554 Acid acceptors, in VDC polymer stabilization, 25 719 Acid-activated bentonites, 6 680-681 Acid amide herbicides, 13 319-320 Acid anhydrides, 10 403-406, 484 reactions with alkanolamines from olefin oxides and ammonia, 2 127 Acid-base catalysis, 5 205-209... 

Acyl chlorides are converted in good yield into symmetrical carboxylic acid anhydrides upon treatment with dilute aqueous sodium hydroxide at -I0°C in the presence of a tetra- -butylammonium salt [76, 77]. Yields are considerably lower when Aliquat is used. In a similar manner, chloroformates and ethyl oxalyl chloride are converted into carbonic hemi-ester anhydrides. 

The C2-symmetrical chiral amine tran.v-(2/ ,6y )-2,6-bis(benzyloxymethyl)piperidine (1), prepared15 from commercially available (S)-2-(benzyloxymethyl)oxirane, has been used in diastereoselective amide alkylations. Thus, the chiral amine of 76% ee is acylated [anhydride or mixed trimethylacetic acid anhydride, 1.2 equivalents of triethylamine and 0.05 equivalents of 4-(dimethylamino)pyridine] and the resulting amide 2 treated with 2.1 equivalents of lithium diisopropylamide at —78 CC to give the enolate. This is then alkylated to give high diastereo-meric ratios (>94 6) of alkylation products 3 in 60-93% yield16. 

Symmetrical acid anhydrides are named by replacing the -acid suffix of the parent carboxylic acids with the word anhydride. Mixed anhydrides that consist of two different acid-derived parts are named using the names of the two individual acids with an alphabetical order. 

Carboxylic acid anhydrides. Carboxylic acids are converted to the symmetrical anhydride by reaction with 1 and triethylaminc in acetone or methylene chloride at room temperature (equation I). 

Ingold518 was the first to propose that nitric acid anhydride N205 has an ionic structure N02+N03. This was later confirmed by Wilson and Christe,519 who showed a linear symmetric N02+ with an N—O bond length of about 1.154 A. The structure of reaction products formed between nitrogen oxides and BF3, including N02+BF4 was established by Olah and co-workers520,521 on the basis of Raman, IR, and X-ray diffraction data. 

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... 

Acid anhydrides result from substituting the acyl group of one acid for the hydroxy hydrogen of another. They are called anhydrides because they can be viewed as resulting from the loss of water from two carboxylic acid molecules (removing H from one and OH from the other). Symmetrical anhydrides derived from two molecules of the... 

Braun et al. studied the polymerization kinetics of symmetrical alkenes, particularly of 4-vinylbenzoic acid anhydride. The cross-linked polymer could be transformed to linear macromolecules by hydrolysis [359]. 

For efficient peptide bond formation acid halides azides 2,b l and Leuchs anhydridesb l were employed as the first activated species in peptide synthesis. Since then, besides considerable improvements to the azide (see Section 3.1) as well as the V-carboxyanhydride 7 procedure d (sgg Section 3.4.3), the methods have evolved over decades along a few basic principles as outlined in Scheme 2. The symmetrical the mixed carboxylic acid 4,b 5s] and the carbonic acid anhydrides were developed and remain useful despite the... 

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... 

Scheme 1 Mixed Carboxylic Acid Anhydrides 1, Mixed Carbonic Acid Anhydrides 2, Symmetrical Anhydrides 3, Al-Carboxyanhydrides 4, iV-Thiocarboxyanhydrides 5, Al-Substituted iV-Carboxyanhydrides 6, and Urethane-Protected Al-Carboxyanhydrides 7...

However, the method is not substantially better than the mixed anhydride method, the standard DCC method, the active ester method, or the newer procedures (HBTU, BOP, PyBroP, etc.), and it uses double the amount of N-protected annino acid to accomplish the condensation reaction. Although many synometrical anhydrides are isolable and stable,t l they are not commercially available. On the other hand, the use of preformed symmetrical anhydrides is very convenient. One needs only to add an annino acid ester to the protected amino acid anhydride in a nonreactive solvent and, upon completion of the condensation, destroy the excess anhydride and remove the acid components by extraction. 

SPPS Coupling with Boc Amino Acids via Symmetrical Anhydrides ... 

SPPS Coupling with Fmoc Amino Acids via Symmetric Anhydrides ... 

---