超声波作用下乙酸辛酯合成条件的研究

在超声波作用下,不用溶剂,以硫酸氢钠为催化剂催化合成乙酸辛酯。最佳反应条件是:正辛醇和乙酸的物质的量比为1∶2.0,催化剂用量为反应物总质量的1.0%,超声时间20min,反应温度84℃。在此反应条件下,酯收率可达80.1%,催化剂可重复使用。     

Rapid esterification of fatty acid using dicationic acidic ionic liquid catalyst via ultrasonic-assisted method

Biodiesel production via esterification/transesterification reactions can be catalyzed by homogenous or heterogeneous catalysts. Development of heterogeneous catalysts for biodiesel production is highly advantageous due to the ease of product purification and of catalyst recyclability. In this current work, a novel acidic [DABCODBS][CF₃SO₃]₂ dicationic ionic liquid (DIL) was used as heterogeneous catalyst to produce biodiesel using oleic acid as model oil. The esterification was conducted under ultrasonic irradiation (20 kHz) using a 14 mm ultrasonic horn transducer operated at various duty cycles. It was observed that the duty cycle, amplitude, methanol to oil molar ratio, catalyst amount and reaction temperature were the major factors that greatly impact the necessary reaction time to lead to a high yield of biodiesel. The reaction conditions were optimized with the aid of Response Surface Methodology (RSM) designed according to the Quadratic model of the Box Behnken method. The optimum conditions were found to be at catalyst amount of 0.64 mol%, methanol to oil ratio of 14.3:1, temperature of 59 °C, reaction time of 83 min and amplitude of 60% in continuous mode. The results showed that the oleic acid was successfully converted into esters with conversion value of 93.20% together with significant reduction of reaction time from 7 h (using mechanical stirring) to 83 min (using ultrasonication). The results also showed that the acidic DIL catalyst we designed purposely was efficient to catalyze the ultrasonic-assisted esterification yielding high conversion of oleic acid to methyl oleate on short times. The DIL was also recycled and reused for at least five times without significant reduction in performance. Overall, the procedure offers advantages including short reaction time, good yield, operational simplicity and environmentally benign characteristics.     

改性ZSM-5分子筛催化合成乙酸戊酯

以ZSM-5为原料,采用浸渍法将其交换成HZSM-5,以HZSM-5为催化剂,对以冰乙酸和正戊醇为原料合成乙酸戊酯的反应条件进行了研究。研究表明,以1.0m ol/L硫酸浸渍后的ZSM-5催化活性最高,当醇酸摩尔比为1.1∶1,催化剂用量为0.4g,反应时间为90m in,反应温度为125—135℃,酯化率可达82.5%。     

Ultrasonic pretreatment for lipase-catalyed synthesis of phytosterol esters with different acyl donors

This study is focused on the enzymatic esterification of phytosterols with different acyl donors to produce the corresponding phytosterol esters catalyzed by Canadia sp. 99-125 lipase under ultrasound irradiation. An ultrasonic frequency of 35 kHz, power of 200 W and time of 1h was determined to guarantee satisfactory degree of esterification and lipase activity. The influence of temperature, substrates concentration and molar ratio was investigated subsequently. The optimum production was achieved in isooctane system at 60°C with phytosterol concentration of 150 μmol/mL and phytosterol to fatty acid molar ratio of 1:1.5, resulting in a phytosterol esters conversion of above 85.7% in short reaction time (8h). Phytosterols esters could also be converted in high yields to the corresponding long-chain acyl esters via transesterification with triacylglycerols (above 90.3%) under ultrasound irradiation. In optimum conditions, the overall esterification reaction rate using the ultrasonic pretreatment process was above 2-fold than that of mechanical stirring process without damage the lipase activity.     

Ultrasound-assisted biodiesel production by a novel composite of Fe(III)-based MOF and phosphotangestic acid as efficient and reusable catalyst

In this work, esterification of oleic acid by various alcohols is achieved with high yields under ultrasonic irradiation. This reaction performed with a novel heterogeneous catalyst that fabricated by heteropoly acid and Fe(III)-based MOF, namely MIL-53 (Fe). Syntheses of MIL-53 and encapsulation process carry out by ultrasound irradiation at ambient temperature and atmospheric pressure. The prepared composite was characterized by various techniques such as XRD, FT-IR, SEM, BET and ICP that demonstrate excellent catalytic activities, while being highly convenient to synthesize. The obtained results revealed that ultrasound irradiation could be used for the appropriate and rapid biodiesel production.     

Esterification of sodium 4-hydroxybenzoate by ultrasound-assisted solid–liquid phase-transfer catalysis using dual-site phase-transfer catalyst

The catalytic esterification of sodium 4-hydroxybenzoate with benzyl bromide by ultrasound-assisted solid–liquid phase-transfer catalysis (U-SLPTC) was investigated using the novel dual-site phase-transfer catalyst 4,4′-bis(tributylammoniomethyl)-1,1′-biphenyl dichloride (BTBAMBC), which was synthesized from the reaction of 4,4′-bis(chloromethyl)-1,1′-biphenyl and tributylamine. Without catalyst and in the absence of water, the product yield at 60 °C was only 0.36% in 30 min of reaction even under ultrasound irradiation (28 kHz/300 W) and 250 rpm of stirring speed. When 1 cm³ of water and 0.5 mmol of BTBAMBC were added, the yield increased to 84.3%. The catalytic intermediate 4,4′-bis(tributylammoniomethyl)-1,1′-biphenyl di-4-hydroxybenzoate was also synthesized to verify the intrinsic reaction which was mainly conducted in the quasi-aqueous phase locating between solid and organic phases. Pseudo-first-order kinetic equation was used to correlate the overall reaction, and the apparent rate coefficient with ultrasound (28 kHz/300 W) was 0.1057 min⁻¹, with 88% higher than that (0.0563 min⁻¹) without ultrasound. The esterification under ultrasonic irradiation using BTBAMBC by solid–liquid phase-transfer catalysis was developed.     

Ultrasound accelerated Claisen-Schmidt condensation: A green route to chalcones

Chalcones have been synthesized under sonochemical irradiation by Claisen-Schmidt condensation between benzaldehyde and acetophenone. Two basic activated carbons (Na and Cs-Norit) have been used as catalysts. The effect of the ultrasound activation has been studied. A substantial enhancing effect in the yield was observed when the carbon catalyst was activated under ultrasonic waves. This “green” method (combination of alkaline-doped carbon catalyst and ultrasound waves) has been applied to the synthesis of several chalcones with antibacterial properties achieving, in all cases, excellent activities and selectivities. A comparative study under non-sonic activation has showed that the yields are lower in silent conditions, indicating that the sonication exerts a positive effect on the activity of the catalyst. Cs-doped carbon is presented as the optimum catalyst, giving excellent activity for this type of condensation. Cs-Norit carbon catalyst can compete with the traditional NaOH/EtOH when the reaction is carried out under ultrasounds. The role of solvent in this reaction was studied with ethanol. High conversion was obtained in absence of solvent. The carbons were characterized by thermal analysis, nitrogen adsorption and X-ray photoelectron spectroscopy.     

Ultrasonic versus silent methylation of vegetable oils

The profile of fatty acid methyl esters (FAME) of different vegetable oils produced under ultrasonic irradiation and conventional heating were compared. In the presence of potassium hydroxide as catalyst, the distribution of FAME was quite similar for both procedures, while in the case of sodium hydroxide ultrasonic irradiation gave better results. The FAME profile resulted from the reaction catalyzed by sulfuric acid was almost the same with the one resulted from the reaction catalyzed by KOH, while boron trifluoride can give rise to many artifacts, thus is not a reliable catalyst.     

An efficient and practical synthesis of mandelic acid by combination of complex phase transfer catalyst and ultrasonic irradiation

Mandelic acid was synthesized from benzaldehyde with chloroform in a 81% yield at 60 degrees C for 2 h by using triethylbenzylammonium chloride (TEBA) and poly(ethylene glycol)-800 (PEG-800) as a complex phase transfer catalyst under ultrasonic irradiation. The main advantages of this present method are that the reaction time is much shorter and the yield is higher than those of the classical method. p-Methoxymandelic acid was also obtained in a 84% yield under the same reaction conditions.     

Ultrasound assisted the chemoselective 1,1-diacetate protection and deprotection of aldehydes catalyzed by poly(4-vinylpyridinium)hydrogen sulfate salt as a eco-benign,efficient and reusable solid acid catalyst

Poly(4-vinylpyridinium) hydrogen sulfate solid acid was found to be efficient catalyst for preparation of 1,1-diacetate using ultrasound irradiation at ambient temperature and neat condition. Deprotection of the resulting 1,1-diacetates were achieved using the same catalyst in methanol solvent under ultrasound irradiation at room temperature. This new method consistently has the advantage of excellent yields and short reaction times. Utilization of solvent free, simple reaction conditions, isolation, and purification makes this manipulation very interesting from an economic and environmental perspective. Further, the catalyst can be reused and recovered for several times.     

Ultrasound accelerated esterification of bile acids

In this study power ultrasound accelerated esterification reactions of some model substances and bile acids were done. In the model reactions the best result was 19-fold increase in the reaction rate when using ultrasound and the temperature was allowed to rise during the irradiation. In the case of bile acid methyl esters a clear increase in the reaction rates was also observed by ultrasonic irradiations.     

Comparative material study and synthesis of 4-(4-nitrophenyl)oxazol-2-amine via sonochemical and thermal method

The present paper deals with the synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as medium. It was observed that ultrasound-assisted method gave 90% yield in just 8 min as against 3.5 h required to get 69% yield by thermal method. One of the compounds 4-(4-nitrophenyl)-1,3-oxazol-2-amine synthesized by both methods were subjected to material characterization study via XRD, TGA and SEM analysis. It was observed that use of ultrasound not only increased the rate of reaction but also improved the quality of product obtained. The crystallinity of the product from ultrasound method was 21.12% whereas thermal method fetched only 8.33% crystallinity thereby improving crystallinity by almost 60%. In addition, sonochemical synthesis also saved more than 70% energy as depicted by energy calculations.     

Ultrasonic-assisted ozone degradation of organic pollutants in industrial sulfuric acid

In this work, a combination of ozone (O₃) and ultrasound (US) has been firstly used to decolorize black concentrated sulfuric acid with high organic content. The effect of different reaction factors on the transparency, extent of decolorization, H₂SO₄ mass fraction, and organic pollutants removal is studied. In addition, the systematic interaction between ultrasound and ozone on the decolorization process is reviewed through comparative experiments of O₃, US and US/O₃. A sulfuric acid product that meets the requirements for first-class products in national standards, with an extent of decolorization of 74.07%, transparency of 70 mm, and a mass fraction of 98.04%, is obtained under the optimized conditions. Under the same conditions, it has been established that the treatment time can be saved by 25% using the US/O₃ process compared to using O₃. Further, the production of oxidative free radicals (•OH) in a concentrated sulfuric acid system is enhanced using the US/O₃ process compared with O₃. In addition, the degree of effectiveness of different oxidizing components on the decolorization process is revealed by adding different free radical shielding agents when the US/O₃ process is used.     

Influence of ultrasonic waves in the reduction of nitrate to nitrite by hydrazine-Cu(II)

Colorimetric methods are still important for determining nitrate and nitrite. A critical step in the use of these methods to determine nitrate in low concentrations is the reaction time required to totally reduce nitrate to nitrite, i.e., 24h in the dark. This work involved a study of the influence of ultrasonic irradiation on the nitrate reduction reaction by hydrazine. Our findings indicated that ultrasonic irradiation, associated with copper(II) ion as a catalyst, increased the redox reaction rate, decreasing the reaction time to about 10min when the power of the ultrasonic irradiation was set in 14.0357W. The strong influence of the ultrasonic irradiation in the reduction reaction rates can be sustained by an excellent linear correlation (R(2)=0.9993) between the kinetic constants and ultrasonic powers. Nitrate conversion also increased from 68% to 98% at the latter conditions. It thus become clear that high intensity ultrasound is very beneficial for this reduction reaction to proceed in good yield and in short reaction time in comparison to its silent reaction.     

Ultrasonically-promoted synthesis of mandelic acid by phase transfer catalysis in an ionic liquid

An efficient and facile process to synthesize mandelic acid through phase transfer catalysis (PTC; also phase transfer catalyst) using ultrasound in an ionic liquid has been developed. Mandelic acid was synthesized from benzaldehyde with chloroform in an 89.6% yield at 60°C for 2h by using tetrabutyl ammonium bromide (TBAB) as a phase transfer catalyst. Effects of different factors, such as frequency of ultrasound, reaction temperature, kinds of PTC and solvents had been investigated to obtain the optimum condition. It was observed that the ultrasonically promoted synthesis of mandelic acid by PTC in the ionic liquid exhibited significant enhancement in reaction yields under ambient conditions.     

Ultrasound assisted two-stage biodiesel synthesis from non-edible Schleichera triguga oil using heterogeneous catalyst: Kinetics and thermodynamic analysis

Present work deals with the ultrasound-assisted biodiesel production from low cost, substantial acid value kusum (Schleichera triguga) oil using a two-step method of esterification in presence of acid (H₂SO₄) catalyst followed by transesterification using a basic heterogeneous barium hydroxide (Ba(OH)₂) catalyst. The initial acid value of kusum oil was reduced from 21.65 to 0.84 mg of KOH/g of oil, by acid catalyzed esterification with 4:1 methanol to oil molar ratio, catalyst concentration 1% (v/v), ultrasonic irradiation time 20 min at 40 °C. Then, Ba(OH)₂ concentration of 3% (w/w), methanol to oil molar ratio of 9:1, ultrasonic irradiation time of 80 min, and temperature of 50 °C was found to be the optimum conditions for transesterification step and triglyceride conversion of 96.8% (wt) was achieved. This paper also examined the kinetics as well as the evaluation of thermodynamic parameters for both esterification and transesterification reactions. The lower value of activation energy and higher values of kinetic constants indicated a fast rate of reaction, which could be attributed to the physical effect of emulsification, in which the microturbulence generated due to radial motion of bubbles, creates an intimate mixing of the immiscible reactants causing the increase in the interfacial area, giving faster reaction kinetics. The positive values of Gibbs-free energy (ΔG), enthalpy (ΔH) and negative value of entropy (ΔS) revealed that both the esterification and transesterification were non-spontaneous, endothermic and endergonic reactions. Therefore, the present work has not only established the escalation obtained due to ultrasonication but also exemplified the two-step approach for synthesis of biodiesel from non-edible kusum oil based on the use of heterogeneous catalyst for the transesterification step.     

Ultrasound assisted enzymatic conversion of non edible oil to methyl esters

Conventional and ultrasound-assisted hydrolysis and subsequent esterification of Nagchampa oil under mild operating conditions have been investigated with an objective of intensification of methyl esters production using a sustainable approach. The effect of ratio of reactants, temperature, enzyme loading, pretreatment of enzyme (using ultrasonic irradiations) on the hydrolysis and esterification reaction has been studied. Optimum conditions for hydrolysis were observed to be 1:1 weight ratio of oil: water for Lip Z and 1:3 for Lip 2 enzymes, enzyme loading of 400 units for Lip Z and 800 mg for Lip 2 enzymes and reaction time of 6 h. In the case of esterification reaction, optimum conditions obtained were oil to methanol molar ratio of 1:2, enzyme loading of 1000 mg and reaction time of 20 h. Use of pretreated enzyme (using ultrasonic irradiations) was found to increase the extent of esterification reaction from 75% to 92.5%. It was observed that use of ultrasound in the reaction significantly intensified the esterification reaction with time requirement reducing from 20 h for conventional stirring based approach to only about 7.5 h in the presence of ultrasound. The extent of esterification obtained with sonicated enzyme also increased to 96% from 75% with unsonicated enzyme.     

Intensification of heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction using ultrasound: Understanding effect of operating parameters

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is a significant reaction for obtaining industrially important products. The current research work deals with intensification of reaction of 4-bromoanisole and phenylboronic acid catalyzed with 5 wt% Pd/C (5% by weight Pd supported on C available as commercial catalyst) using ultrasound and more importantly, without use of any additional phase transfer catalyst. Heterogeneous catalyst has been selected in the present work so as to harness the benefits of easy separation and the possible limitations of heterogeneous operation are minimized by introducing ultrasonic irradiations. The effect of operating parameters such as ultrasound power, temperature, catalyst loading and molar ratio on the progress of reaction has been investigated. It has been observed that an optimum power, temperature and catalyst loading exist for maximum benefits whereas higher molar ratio was found to be favourable for the progress of the reaction. Also, the use of ultrasound reduced the reaction time from 70 min required in conventional approach to only 35 min under conditions of frequency of 22 kHz, power dissipation of 40 W and catalyst loading as 1.5 mol% (refers to total quantum of catalyst used in the work) in ethanol-water system under ambient conditions. The work also demonstrated successful results at ten times higher volume as compared to the normally used volumes in the case of simple ultrasonic horn. Overall, the work has successfully demonstrated process intensification benefits obtained due to the use of ultrasound for heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction.     

石墨烯固体酸催化转化葡萄糖为化学品

利用氢化钠和丙磺酸内酯合成出了磺化石墨烯催化剂,采用XPS、FT-IR、TEM等方法对其进行了表征,并且对此催化剂催化葡萄糖的转化反应进行了研究．探究此催化剂在纯水中、没有添加任何有机溶剂下催化转化葡萄糖制备高附加值化学品方面的催化活性,在最优的反应条件下, 5-羟甲基糠醛(HMF)最高产率可达28.8%,产物甲酸、乳酸和HMF的总产率可达51.94%．经过5次催化反应,催化剂仍表现出相对高的催化活性,三种产物的产率依然较高,表明此种固体酸催化剂有很好的热稳定性．     

Propargylation of indene-1,3-dione under a new phase-transfer catalyst combined with ultrasonication – A kinetic study

In the present study, kinetics of synthesis of 2,2-di(prop-2-ynyl)-1H-indene-1,3(2H)-dione was successfully carried out by propargylation of indene-1,3-dione with propargyl bromide using aqueous potassium hydroxide and catalyzed by a newly synthesized phase-transfer catalyst viz., N-benzyl-N-ethyl-N-isopropylpropan-2-ammonium bromide, PTC under ultrasonic (40 kHz, 300 W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40 kHz, 300 W) in a batch reactor, it shows that the overall reaction rate can be greatly enhanced with ultrasound irradiation than without ultrasound.