Recent developments in methods for the esterification and protection of the carboxyl group

The chemistry of the carboxyl group is one of the cornerstones of organic chemistry. As a consequence two very important facets of synthetic methodology are the activation of the carboxyl group to facilitate esterification and the d'eactivation or masking of the carboxyl group during a synthetic sequence. Some of the more recent innovations and techniques which have been developed in the past 10–15 years around these features of carboxyl group chemistry are discussed in this review.     

Study of the drying behavior of model latex blends during film formation: influence of carboxyl groups

Latex blending is a strategy used to eliminate volatile organic compounds from latex coatings formulations. This paper focuses on the study of the drying kinetics of model hard/soft latex blends and the influence of the presence of carboxyl groups on these particles as well as the extent of neutralization of the carboxyl groups with different bases. The model latex blend was comprised of clean, well‐defined polystyrene hard and poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) soft latex particles with monodisperse particle sizes, homogeneous copolymer composition, and independent control of particle size and carboxyl group content. Drying models are discussed. It was found that the presence of carboxyl groups in the latex particles retarded the drying rate of the model latex blends. When the carboxyl groups present in the latex blends with low carboxyl group coverage on polystyrene particles were neutralized by using ammonium hydroxide or sodium hydroxide, the drying rate increased. When the carboxyl groups present in the latex blends with a high carboxyl group coverage on polystyrene particles were neutralized by sodium hydroxide, potassium hydroxide, or cesium hydroxide, the drying rate first decreased and then increased as the extent of the neutralization increased. However, the neutralization of these carboxyl groups with ammonium hydroxide increased the drying rate of the latex blends within a broad range of neutralization conditions (from 0 to 100%). A cluster model was proposed to explain these phenomena.     

New peptide synthesis using the ozonolysate of 2-(1-phthalimido)alkyl-5-phenyloxazoles

It was proved that 2-(1-phthalimido)alkyl-5-phenyloxazoles 3 were useful synthetic intermediates for peptide synthesis, where the oxazole ring acted as not only the carboxyl protecting group but also the carboxyl activating group upon ozonolysis.     

Cationic ring-opening transfer polymerization of spiro ortho esters initiated by carbon black

The ring-opening transfer polymerization of spiro ortho esters (SOE) initiated by carbon black was investigated. In the absence of carbon black, no polymerization occurred at all. In the presence of channel black containing carboxyl group, the ring-opening transfer polymerization of SOE was initiated at 50-70°C. to give polyether ester, namely alternating copolymer of epoxide and lactone. The rate of polymerization of 1,4,6-trioxaspiro[4.4]nonane and 1,4,6-trioxaspiro[4.5]decane was considerably small compared with that of 1,4,6-trioxaspiro[4.6]undecane. The activation energy of the polymerization of 2-chloromethyl-1,4,6-trioxaspiro[4.6]undecane was estimated to be 6.0 kcal/mol. The initiating activity of carbon black increased with an increase in carboxyl group content of carbon black. Furnace black that contained no carboxyl group was unable to initiate the polymerization. Furthermore, the carbon black lost the initiating ability of the polymerization upon the blocking of carboxyl group on the surface by the treatment with potassium hydroxide or diazomethane. Based on these results, it was concluded that carboxyl group on carbon black plays an important role in the initiation. During the polymerization, a part of the polymer formed was grafted onto carbon black: the grafting ratio was 10–30%. The mechanisms of initiation and grafting were discussed.     

羧基导向C―H官能团化/脱羧偶联反应研究进展

以邻或对位取代苯甲酸为原料,通过羧基导向的芳香羧酸邻位碳氢键官能团化继而发生脱羧反应,在原羧基的邻位引入官能团,可以合成传统付-克反应难以合成的间位取代芳香化合物。在此类反应中,羧基充当无痕导向基的功能。本文综述了基于过渡金属催化羧基无痕导向的芳香羧酸脱羧偶联策略,形成新C―C、C―杂键的研究进展。     

Simultaneous protection and activation of amino acids using propargyl pentafluorophenyl carbonate

[reaction: see text] A very efficient method for the simultaneous protection of the amino group and activation of the carboxyl group of amino acids is reported using propargyl pentafluorophenyl carbonate (PocOPfp). The amino group is protected as a propargyloxycarbonyl (Poc) derivative, and the carboxyl group is activated as a pentafluorophenyl ester. The yields obtained are good to excellent ranging from 60 to 87%.     

酶促合成肽的研究 II: 含羧基侧链氨基酸的肽的酶促合成

用嗜热菌酶酶促合成了一系列含门冬氨酸、谷氨酸的肽. 实验证明, 缩合反应中羧基组份中的门冬氨酸β-羧基或谷氨酸γ-羧基毋需保护. 同时也研究了邻近氨基酸残基对缩合反应的影响.     

Effect of carboxyl end groups on hydrolysis of polyglycolic acid

Dye interaction analysis in hexafluoroisopropanol was used to determine end carboxyl groups in polyglycolic acid (PGA). The rate of heterogeneous hydrolysis of purified PGA in water at 37°C shows a first-order dependence on carboxyl end group concentration at levels above 12 meq/kg. Reaction of molten PGA with a tetraarylorthocarbonate or a triarylketenimine gave end-capped PGA with carboxyl levels as low as 1 meq/kg. These samples were somewhat more resistant to hydrolysis than untreated PGA despite an increased initial rate at the lower carboxyl levels.     

Novel dual-mode photoresist based on decarboxylation by photogenerated base compound

The copolymers containing a carboxyl group were used as the two-component photopolymers in combination with dimethyl 4-(o-nitrophenyl)-2,6-dimethyl-1,4-dihydro-3,5-pyridinedicarboxylate (NMHP) as a photobase generator. Under irradiation by 365 nm light, NMHP is converted to dimethyl 4-(o-nitrosophenyl)-2,6-dimethyl-3,5-pyridinedicarboxylate (NMP). NMP acts as a base catalyst for the thermal decarboxylation of a carboxyl group in the polymer. The decarboxylation in the polymer provides a negative-working photoresist under the additional flood-exposure of 365 nm light before development. This process is called the photoassisted contrast (PAC) process. NMHP acts as a dissolution inhibitor for the aqueous base development of the polymers containing a carboxyl group but NMP promotes the dissolution of the polymers. This change in the solubility inhibition of NMHP offers a positive-working photoresist without the process of post-exposure baking (PEB) and the PAC process. Therefore, NMP, the photoproduct of NMHP, produces dual-tone-mode photoresists with the copolymers containing a carboxyl group. © 1998 John Wiley & Sons, Ltd.     

Synthesis and spectroscopic studies of 3-carbamoylisonicotinic acid derivatives

An unusual example of the selective hydrolysis of a cyano group to the corresponding carboxyl group under mild reaction conditions in the presence of a carboxamide group is reported. The reaction resulted in the formation of a rare combination of vicinal carboxamide and carboxyl groups on a pyridone ring. The structure of the synthesized products was thoroughly studied using one- and two-dimensional NMR experiments and the reaction pathway was monitored fluorometrically.     

Separation of enantiomers on a chiral stationary phase based on ovoglycoprotein: V. Influence of immobilization method on chiral resolution

Ovoglycoprotein from chicken egg whites (OGCHI) was bound to aminopropyl-silica gels via an amino or carboxyl group(s) of OGCHI. In the former case, OGCHI was bound to N,N′-disuccinimidyl carbonate-activated aminopropyl-silica gels, while in the latter case OGCHI activated by a water-soluble carbodiimide and N-hydroxysulfosuccinimide was bound to aminopropyl-silica gels. The obtained OGCHI materials were compared with regard to the bound amounts, retentivity and enantioselectivity. The OGCHI materials prepared via a carboxyl group(s) of OGCHI are suitable for chiral resolution of acidic solutes, and those via an amino group(s) of OGCHI are suitable for chiral resolution of basic solutes. It is suggested that the electrostatic interaction between an amino or carboxyl group of OGCHI and a charged solute should play an important role in chiral recognition of the solute.     

Simple and efficient synthesis of new tricarboxylic acids bearing cyclohexane and norbornane fragments

A synthesis new aryl alicyclic tricarboxylic acids bearing two carboxyl groups at either cyclohexane or norbornane fragment and one carboxyl group at the benzene ring was devel-oped. Tricarboxylic acids of this type are promising monomers for the synthesis of hetero-cyclic polymers.     

电导滴定法对苯乙烯/丙烯酸无皂乳液共聚微球表面性质的研究

本文主要叙述用电导滴定法对羧化微球表面的羧基含量进行了测定,以便了解其表面特性与IgG吸附的关系,进而获得满意的微球产品。     

Cationic ring-opening isomerization polymerization of spiro orthocarbonates initiated by carbon black

The ring-opening isomerization polymerization of spiro orthocarbonates (SOC), such as 2,8-dimethyl-1,5,7,11-tetraoxaspiro[5.5]undecane ( I ), 8,10,19,20-tetraoxaspiro[5.2.2.5.2.2]-heneicosane-2,4-diene ( II ), and 8,10,19,20-tetraoxaspiro[5.2.2.5.2.2]heneicosane ( III ), initiated by carbon black was investigated. No polymerization of SOC was initiated in the absence of carbon black. But in the presence of channel black having a carboxyl group, the polymerization of SOCs was initiated at 90–150°C to give the corresponding polyether carbonates. The initiating ability of carbon black increased with an increase in its carboxyl group content. Furnace black having no carboxyl group failed to initiate the polymerization. Based on these results, it was concluded that the carboxyl group on carbon black is capable of initiating the polymerization of SOC. During the polymerization, a part of the polymers formed was grafted onto carbon black surface via the termination of growing polymer chains. The percentage of grafting increased with an increase in conversion and reached about 55%. Furthermore, polyether carbonate-grafted carbon black was found to produce a stable colloidal dispersion in chloroform. The mechanism of initiation and grafting were discussed.     

Solubility enhancement for poly(amic acid)s by rapid hydrolysis of the polymer main chain during alkaline development

In an alkaline developer carboxyl containing polymer films possess a higher critical carboxyl group concentration (CGC₀) below which dissolution does not occur, compared with novolac resins; therefore, it is difficult to obtain the polymer film with a lower dissolution rate and less swelling. We describe herein a new approach for reducing CGC₀ of carboxyl containing polymers by introducing an ester group which is labile in the alkaline developer within the time‐scale of development to obtain the polymers with moderate dissolution rates and less swelling. The rapid hydrolysis that leads to polymer degradation is clearly verified by gel permeation chromatography (GPC).     

The thermo-oxidative degradation of polyolefines—Part 10. Correlation between the formation of carboxyl groups and scission in the oxidation of polyethylene in the melt phase

Films of low density polyethylene have been degraded under an oxygen atmosphere at temperatures above the semicrystalline melting point. Time, conversion and temperature dependence of carboxyl group formation and chain scission have been studied. After induction periods we found linear dependences both in function of time and conversion. One third of absorbed oxygen forms carboxyl groups and the absorption of 3·57 mmol oxygen per monomer unit is needed for one chain scission. Maximum rates of carboxyl formation and chain scission have Arrhenius temperature dependence with 33·5 kcal/mole activation energy. The number of carboxyl groups and chain scissions are always practically the same; we assume that the isomerisation of secondary alkyl peroxy radicals simultaneously causes chain scission and carboxyl formation.     

trans‐4‐Acetylcyclo­hexane­carboxyl­ic acid and ()‐trans‐2‐acetyl­cyclo­hexane­carboxyl­ic acid: hydrogen‐bonding patterns in two isomeric keto acids

Both title compounds, C₉H₁₄O₃, display carboxyl‐dimer hydrogen‐bonding patterns. The 4‐acetyl isomer adopts a chiral conformation with negligible disordering of the methyl and carboxyl groups and forms centrosymmetric dimers across the b and c edges of the chosen cell [O?O = 2.667 (3) Å and O—H?O = 175°]. Intermolecular C—H?O close contacts were found for both carbonyl groups. In the 2‐acetyl isomer, there is no intramolecular interaction between the carboxyl and acetyl groups and the hydrogen bonding involves centrosymmetric carboxyl dimerization across the ab and ac faces of the chosen cell [O?O = 2.668 (2) Å and O—H?O = 173°]. The carboxyl group is negligibly disordered, but significant rotational disordering was found for the acetyl methyl group. An intermolecular C—H?O close contact was found involving the ketone group.     

A theoretical study of malonate and formate calcium binding by ab initio techniques

Ab initio calculations at the STO—3G level have been performed on the binding of CA(II) ion to malonate and formate with and without d orbitals in the basis set for the CA(II) ion. The malonate and formate binding results with CA(II) are similar. The addition of d orbitals to CA(II) has little effect on the conformational minimum. The results are qualitatively similar to those from our previous calculations on the Mg²⁺—malonate interaction: a single carboxyl interaction with the metal ion appears to be preferred over a conformation in which two carboxyl groups bind to Ca(II). Moreover, the single carboxyl group interaction with CA(II) appears to be favored over the binding of CA(II) to a single oxygen of a carboxyl group.     

α-氨基酸在水-乙醇中羧基质子化热力学

Enthalpy changes for the protonation of carboxyl group of four α-amino acids(glycine,L-α-alanine,L-valine and L-serine) were measured in water-ethanol mixtures (10－ 70wt％) at 298.15K using LKB-2277 Bioactivity Monitor.The corresponding entropy and Gibbs energy changes were also calculated.The results show that both enthalpy changes and entropy changes are favorable to the protonation of carboxyl groups of the investigated amino acids in water-ethanol mixtures.However,the influence of the composition of ethanol in the mixed solvents on the enthalpy change and entropy changes is complicated.Both sδ and sδ ,the differences of enthalpy changes and entropy changes in mixed solvents and in pure water respectively,show a minimum approximately at xEtOH=0.1.The effects of side chains on the enthalpy change and entropy changes were also investigated using the proton transfer process between glycine and the other three amino acids.The results demonstrate that the proton transfer processes for alanine and valine are spontaneous but not for serine,which could be interpreted in terms of the electrostatic interaction between amino group and carboxyl group within the molecule and the interaction between carboxyl group and the solvent.     

利用X射线光电子能谱研究马家塔煤显微组分中氧的赋存形态

煤中氧的赋存形态是煤结构研究的重要内容，煤炭加工转化（如煤的热解、直接加氢液化等）也需要确实详尽的煤中氧赋存形态的数据信息。x射线光电子能谱法（x—ray Photoelectron Speetroscopy，XPS）是近年来新出现的最有效的元素分析方法之一，目前，已在化学、物理、生物等各个领域中得到广泛应用。1974年，XPS分析方法首次用于煤的研究，近年来，XPS成为研究煤中硫和氮存在形态的有效方法之一。许多学者在煤中无机矿物中碳、氧、硫的存在形态及XPS直接测定煤中有机硫等方面做过较多研究工作，但由于煤结构的复杂性、实验条件不尽相同以及煤中矿物的干扰等，以往的研究结果并不完全相同。