- Investigating homogeneous Co/Br-/H2O2 catalysed oxidation of lignin model compounds in acetic acid
-
Oxidation of α-O-4, β-O-4 and monomeric lignin model compounds by Co/Br-/H2O2 in acetic acid at 70 °C was investigated. Co and Br- were introduced as cobalt acetate tetrahydrate and KBr respectively. The degree of methoxylation of the substrate was found to affect its reactivity. For the α-O-4 model compounds, increased methoxylation of the benzyl moiety influenced product selectivity, while increased methoxylation of the phenolic moiety increased substrate conversion. The β-O-4 model compounds exhibited similar conversions to the α-O-4 models, but afforded a lesser amount of monomeric products. The formation of phenol and guaiacol from α-O-4 bond cleavage inhibited substrate conversion and sequestered oxidation products due to the formation of phenoxy radicals and polyguaiacols. Similar to the α-O-4 model compounds, increased methoxylation of the monomers changed the types of products formed, from polyphenols (phenol and guaiacol) to quinones (syringol). The behaviour of syringol was explored extensively, revealing that the corresponding 1,4-hydroquinone strongly inhibited syringol oxidation, and the syringol oxidation product, 4,4′-diphenoquinone, was susceptible to over-oxidation. The deleterious effects of phenols on oxidation of an α-O-4 model could be reduced by substitution of the Br- co-catalyst with N-hydroxyphthalimide (NHPI), improving substrate conversion and product selectivity.
- Clatworthy, Edwin B.,Picone-Murray, Julia L.,Yuen, Alexander K. L.,Maschmeyer, Richard T.,Masters, Anthony F.,Maschmeyer, Thomas
-
p. 384 - 397
(2019/01/28)
-
- Selective acetylation of primary alcohols by ethyl acetate
-
A KOtBu and ethyl acetate mediated efficient methodology has been developed for the acetylation of primary and secondary alcohols where ethyl acetate is the source of acetyl group. The reaction is fast, mild, efficient, and highly selective towards the primary alcohols.
- Singha, Raju,Ray, Jayanta K.
-
p. 5395 - 5398
(2016/11/11)
-
- Electrogenerated N-heterocyclic carbenes in the room temperature parent ionic liquid as an efficient medium for transesterification/acylation reactions
-
N-Heterocyclic carbenes (NHCs), generated by electrochemical reduction under galvanostatic control of 1,3-dialkylimidazolium-based ionic liquids, were employed as catalysts in transesterification reactions in the parent, room temperature ionic liquids (RTILs) as solvents, without the utilisation of any volatile organic solvent or base. The reaction between isopropenyl or ethyl acetate and an alcohol (not efficient in the absence of catalyst) was induced by the presence of an electrogenerated NHC, which seems to assist the proton transfer from the alcohol to the ester, yielding the corresponding acetate. The reaction also proceeds with methyl nicotinate as starting ester and 2-(diethylamino)ethanol or benzyl alcohol as alcohols and leads to the corresponding biologically active compounds, nicametate and benzyl nicotinate, in good yields. All products were isolated in good to excellent yields and complete recyclability of the ionic liquid as solvent has been demonstrated.
- Chiarotto, Isabella,Feroci, Marta,Sotgiu, Giovanni,Inesi, Achille
-
supporting information
p. 326 - 331
(2013/02/25)
-
- One-pot sequence for reductive-acetylation of carbonyl compounds with (N-methylimidazole)(tetrahydroborato)zinc complex
-
Reductive-acetylation of variety of aliphatic and aromatic aldehydes and ketones, α,β-unsaturated carbonyl compounds are examined efficiently with (N-methylimidazole)(tetrahydroborato)zinc complex, [Zn(BH4) 2(nmi)], under mild condition in THF at room temperature or reflux conditions. The corresponding acetates were obtained in excellent yields (90-98 %).
- Setamdideh, Davood,Khezri, Behrooz
-
experimental part
p. 5766 - 5772
(2012/07/28)
-
- Trialkylsilyl triflimides as easily tunable organocatalysts for allylation and benzylation of silyl carbon nucleophiles with non-genotoxic reagents
-
Trialkylsilyl triflimides generated in situ are unique catalysts for the electrophilic benzylation or allylation of trialkylsilylenol ethers or allyl trialkylsilanes with non-genotoxic alkylating reagents such as benzyl and allyl acetates. In most cases the reactions are fast at room temperature and yields are high. The reaction works particularly well with electron-rich benzyl donors including derivatives of pyrrole, indole and furane.
- Mendoza, Oscar,Rossey, Guy,Ghosez, Léon
-
supporting information; experimental part
p. 2571 - 2575
(2010/06/21)
-
- Simple and efficient method for acetylation of alcohols, phenols, amines, and thiols using anhydrous NiCl2 under solvent-free conditions
-
Solvent-free acetylation of alcohols, phenols, amines, and thiols with acetic anhydride (Ac2O) in the presence of 0.1mol% (13mg) anhydrous NiCl2, an inexpensive and easily available catalyst, is described. Excellent yields, short reaction time, and mild reaction conditions are important features of this method.
- Meshram, Gangadhar,Patil, Vishvanath D.
-
experimental part
p. 4384 - 4395
(2010/04/29)
-
- Separation, recovery and reuse of N-heterocyclic carbene catalysts in transesterification reactions
-
A novel and convenient strategy to separate, recover and reuse N-heterocyclic carbene catalysts in transesterification reactions has been developed.
- Zeng, Tieqiang,Song, Gonghua,Li, Chao-Jun
-
supporting information; experimental part
p. 6249 - 6251
(2010/02/16)
-
- The unusual characteristics of the aerobic oxidation of 3,4-dimethoxytoluene with metal/bromide catalysts
-
DMtoluene (3,4-dimethoxytoluene; DM = 3,4-dimethoxy), a model compound for lignin oxidation, can be autoxidized in acetic acid using a Co/Mn/Br catalyst to its benzaldehyde in 51 mol % yield, and to its acid in 85-92 mol % yield. This synthesis is unusual because a number of unprecedented phenomena occur. 1) The rate of molecular oxygen reacting with the substrate is bi-phasic, i.e., two maximum in the rate of reaction are observed. 2) In the first phase, all of the 3,4-dimethoxytoluene is converted to intermediates, but very little to the carboxylic acid. 3) During the second maximum of activity, virtually all the intermediates are converted to the carboxylic acid with 95-100% mass accountability. 4) The rate of carbon monoxide and carbon dioxide formation is considerably higher during the second phase during which 5) 9-12% of methyl 3,4-dimethoxybenzoate (the methyl ester of the benzoic acid) is formed. Mechanisms are suggested for these unusual phenomena.
- Partenheimer, Walt
-
p. 1495 - 1500
(2007/10/03)
-
- Electrostatic catalysis by ionic aggregates: Scope and limitations of Mg(ClO4)2 as acylation catalyst
-
Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO4) 2>Ba(ClO4)2>LiClO4. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO4) 2. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.
- Chakraborti, Asit K.,Sharma, Lalima,Gulhane, Rajesh,Shivani
-
p. 7661 - 7668
(2007/10/03)
-
- Liquid phase acylation of alcohols with acetic acid over zeolites
-
The liquid phase acylation of primary and secondary alcohols were carried out with acetic acid in the presence of zeolites. LaY zeolite is found to be the best catalyst.
- Narender,Srinivasu,Kulkarni,Raghavan
-
p. 1887 - 1893
(2007/10/03)
-
- Oxidative decarboxylation of arylacetic acids with manganese(III) acetate
-
The oxidative decarboxylation reactions of arylacetic acids to arylcarbinols were compared for Mn(III) acetate, Ce(IV) ammonium nitrate and a combination reagent of Co(III) acetate-Cu(II) acetate. The reaction with Mn(III) acetate in acetic acid gave the corresponding arylcarbinyl acetate usually in good yield. The reaction was particularly easy when the substrate carried an electron-donating group at the para position of the aromatic ring, or when the acid was secondary or tertiary. In contrast, the product generated with the other reagents was either a mixture containing over- oxidation products or products formed via a different route.
- Mohri, Kunihiko,Mamiya, Junko,Kasahara, Yuka,Isobe, Kimiaki,Tsuda, Yoshisuke
-
p. 2218 - 2222
(2007/10/03)
-
- The Photochemistry of Methoxy-Substituted Benzyl Acetates and Benzyl Pivalates: Homolytic vs Heterolytic Cleavage
-
The multiple methoxy-substituted benzyl acetates (3g-i) and benzyl pivalates (4g-i) have been photolyzed in methanol solution.The products of these reactions are derived from two critical intermediates; the benzyl radical/acyloxy radical pair and the benzyl cation/carboxylate anion pair.As predicted by the meta effect, the yield of ion-derived product, the methyl ether in this case, was enhanced by the presence of the m-methoxy groups.The yield of ether, for the acetate esters, varied from 2percent for the 4-methoxy-substituted ester to 66percent for the 3,4,5-trimethoxy-substituted ester.In contrast, the yield of ether, for the pivalate esters, varied from 1percent for the 4-methoxy-substituted ester to 20percent for the 3,4,5-trimethoxy-substituted one.The meta effect does not explain these differences; electron transfer converting the radical pair to the ion pair is still an important pathway in the mechanism for ion formation.A quantitative analysis of the yield of the ethers was done in order to obtain the electron-transfer rate constants.This analysis revealed that the yield of the ethers was higher than expected based on previous results for other substituted benzyl acetates.A possible explanation for this discrepancy is that internal return of the radical pair to starting material for the acetate esters is more efficient than for the pivalate esters.Also, the esters 3k and 3l, were prepared to study the effect of electron-withdrawing groups in the meta position.For these esters, the benzylic cleavage reactions were inefficient and an isomerization reaction, the benzvalene rearrangement, was competitive.
- Pincock, J. A.,Wedge, P. J.
-
p. 5587 - 5595
(2007/10/02)
-
- Cleavage or acetyl-de-alkylation of 4-methoxybenzyl (mpm) ethers using acetic acid
-
Aryl (4-methoxyphenyl)methyl (MPM) ethers are cleaved by heating with acetic acid for a few hours at 90°C, producing the corresponding phenols and (4-methoxyphenyl)methyl acetate. Under the same conditions alkyl MPM ethers are transformed directly into the corresponding alkyl acetates.
- Hodgetts,Wallace
-
p. 1151 - 1155
(2007/10/02)
-
- Iron porphyrin catalyzed oxidation of lignin model compounds: the oxidation of veratryl alcohol and veratryl acetate
-
meso-Tetra(2,6-dichloro-3-sulfonatophenyl)porphyrin iron chloride catalyzes the oxidation of 3,4-dimethoxybenzyl alcohol (veratryl alcohol) in aqueous solution to give veratraldehyde along with demethoxylation and ring-cleavage products.The isolation of a direct ring-cleavage product from the oxidation of veratryl acetate in aqueous solution supports the previously proposed ring-cleavage mechanisms.The oxidation in methanol, however, does not lead to ring-cleavage products.When veratryl alcohol was oxidized in methanol, solvent was found to be incorporated into the 3-position of veratryl alcohol, giving new insight into the mechanism of oxidation.
- Cui, Futong,Dolphin, David
-
p. 2314 - 2318
(2007/10/02)
-
- The Reactions of Lignin with Alkaline Hydrogen Peroxide. Part III. The Oxidation of Conjugated Carbonyl Structures
-
The alkaline hydrogen peroxide oxidation of aryl-α-carbonyl structures and cinnamaldehyde structures related to lignin has been studied using a kinetic method.Aryl-α-carbonyl structures in phenolic units are quantitatively cleaved to form the corresponding hydroquinone derivatives with rates of reaction strongly dependent on the substitution pattern in the aromatic ring.The presence of heavy metal ions like Fe(III) or Mn(IV) accelerates the oxidation but decreases the yield of hydroquinone.In nonphenolic units the oxidation of aryl-α-carbonyl structures is dependent upon the structure of the side chain.Cinnamaldehyde structures of the coniferaldehyde type are readily cleaved by alkaline hydrogen peroxide giving rise to the corresponding aromatic aldehyde.The reaction shows a first-order dependency on 2-> whereas -> has a negligible influence within the pH range studied.The significance of these results for the bleaching of mechanical pulps with alkaline hydrogen peroxide is briefly discussed.
- Gellerstedt, Goeran,Agnemo, Roland
-
p. 275 - 280
(2007/10/02)
-