Relationship between nitrogen content in grapes and volatiles,namely heavy sulphur compounds,in wines

Ammonium salts were added to white grape musts, before alcoholic fermentation, in order to evaluate their influence on the heavy sulphur compound and aliphatic higher alcohol composition of resulting wines. Six grape musts were used (Trajadura, Pedernã, Loureiro, Azal Branco, Avesso and Alvarinho). Ammonium supplementation of Trajadura and Pedernã grape musts, with the highest nitrogen level, did not influence the content of heavy sulphur compounds and aliphatic higher alcohols in wines; however, the addition of ammonium salts to grape musts with low initial nitrogen content, such as Loureiro, Azal Branco and Avesso, led to a higher production of 1-propanol and a lower production of isoamyl alcohols and sulphur compounds, e.g. S-methyl thioacetate, 2-mercaptoethanol, acetic acid-3-(methylthio)propyl ester, 3-mercapto-1-propanol, 4-(methylthio)-1-butanol, 3-(ethylthio)-1-propanol, 3-methylthiopropionic acid and N-3-(methylthiopropyl)acetamide. For Alvarinho grape must, a decrease in sulphur compound concentrations in wines was only observed for 3-methylthiopropionic acid, acetic acid-3-(methylthio)propyl ester and 2-mercaptoethanol.     

Quantitative analysis of volatiles in transesterified coconut oil by headspace-solid-phase microextraction-gas chromatography–mass spectrometry

A simple and fast headspace-solid-phase microextraction (HS-SPME) method coupled with gas chromatography–mass spectrometry (GC–MS) was developed for the analysis of volatile compounds in transesterified coconut oil by applying solvent dilution. Solvent dilution conditions (solvent type and solvent amount) and HS-SPME sampling parameters (adsorption temperature and time) were optimised through monitoring the adsorption result of the selected volatiles (octanoic acid esters) in transesterified coconut oil samples. The incubation of methanol (800 μl)-diluted oil (200 μl) sample at 60 °C for 30 min led to the best result. The method was further validated by determining the calibration linear range, correlation coefficient (R²), accuracy, precision, limit of detection and limit of quantification through spiking standards into the blank matrix consisting of coconut oil and methanol. This method may also be applicable for detection and determination of volatile compounds in other transesterified oil samples.     

纤维素类生物质合成多元醇的研究进展

随着化石能源的日益耗竭,可再生的生物质能源成为最理想的替代能源。通过催化转化的方法将生物质转变为重要的工业原料是解决能源危机的有效手段。多元醇作为一种重要的工业原料,可以用来合成氢气、液体燃料和化学品。作为自然界最为丰富的生物质,纤维素可以通过催化转化的方法转变为多元醇。本文对纤维素类生物质合成多元醇的方法及研究进展进行了评述,提出了一步法水解/氢化和直接氢化法为纤维素类生物质合成多元醇的可能的发展方向。     

Cu系催化剂在醇类脱氢反应中的应用研究进展

Cu系催化剂具有选择性高、活性高、副产物少、使用温度低、制备工艺耗能低等优点,广泛的应用于醇类脱氢的反应中.文中阐述了Cu系催化剂脱氢反应的机理,及其在不同醇类脱氢反应中的应用研究进展.     

Acid‐Catalyzed Synthesis of α,β‐Disubstituted Conjugated Enones by a Meyer–Schuster‐Type Rearrangement in Allenols

A novel, direct and simple methodology to gain access to α,β‐disubstituted conjugated enones from α‐allenols in a sustainable metal catalysis context, considering the inexpensiveness and environmentally friendliness of iron(III) species and protons, has been developed.

     

Second‐Generation Paracyclophane Imine Ligands for the Dialkylzinc Addition to Aldehydes. Optimization of the Branched Side Chain leads to Improvement for Aliphatic Aldehydes

Two novel diastereomeric [2.2]paracyclophane ketimine ligands (S_P,S)‐ 2 and (R_P,S)‐ 2 , which unite a planar chiral element and a central chiral element, were used towards the enantioselective diethylzinc addition onto aliphatic aldehydes. These improved second‐generation ligands, which are stable in air and water and are easy to obtain, showed significant improvements with respect to the ligands that were previously used.     

A Homogeneous Catalyst for Reduction of Optically Active Esters to the Corresponding Chiral Alcohols without Loss of Optical Purities

A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations – reaction, concentration, and purification – that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted.     

[{W(O)(O2)2(H2O)}2(μ‐O)]2–‐Catalyzed Epoxidation of Allylic Alcohols in Water with High Selectivity and Utilization of Hydrogen Peroxide

A dinuclear peroxotungstate, K₂[{W(O)(O₂)₂(H₂O)}₂(μ‐O)]⋅2 H₂O, exhibits high catalytic performance for the epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide at 305 K in water solvent. The effectiveness of this system is evidenced by high chemo‐, regio‐, and diastereoselectivity, and stereospecificity for the epoxidation of allylic alcohols. Furthermore, products/catalyst separation can be easily carried out by simple extraction and the catalyst recovered can be reused with the maintenance of the catalytic performance.