- Comparison of pyrazines formation in methionine/glucose and corresponding Amadori rearrangement product model
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The generation of pyrazines in a binary methionine/glucose (Met/Glc) mixture and corresponding methionine/glucose-derived Amadori rearrangement product (MG-ARP) was studied. Quantitative analyses of pyrazines and methional revealed that MG-ARP generated more methional compared to Met/Glc, whereas lower content and fewer species of pyrazines were observed in the MG-ARP model. Comparing the availability of α-dicarbonyl compounds generated from the Met/Glc model, methylglyoxal (MGO) was a considerably effective α-dicarbonyl compound for the formation of pyrazines during MG-ARP degradation, but glyoxal (GO) produced from MG-ARP did not effectively participate in the corresponding formation of pyrazines due to the asynchrony on the formation of GO and recovered Met. Diacetyl (DA) content was not high enough to form corresponding pyrazines in the MG-ARP model. The insufficient interaction of precursors and rapid drops in pH limited the formation of pyrazines during MG-ARP degradation. Increasing reaction temperature could reduce the negative inhibitory effect by promoting the content of precursors.
- Cui, Heping,Deng, Shibin,Hayat, Khizar,Ho, Chi-Tang,Zhai, Yun,Zhang, Qiang,Zhang, Xiaoming
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- Characteristic flavor formation of thermally processed N-(1-deoxy-α-D-ribulos-1-yl)-glycine: Decisive role of additional amino acids and promotional effect of glyoxal
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The role of amino acids and α-dicarbonyls in the flavor formation of Amadori rearrangement product (ARP) during thermal processing was investigated. Comparisons of the volatile compounds and their concentrations when N-(1-deoxy-α-D-ribulos-1-yl)-glycine r
- Zhan, Huan,Cui, Heping,Yu, Junhe,Hayat, Khizar,Wu, Xian,Zhang, Xiaoming,Ho, Chi-Tang
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- Reactivity of borohydride incorporated in coordination polymers toward carbon dioxide
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Borohydride (BH4-)-containing coordination polymers converted CO2into HCO2-or [BH3(OCHO)]-, whose reaction routes were affected by the electronegativity of metal ions and the coo
- Kadota, Kentaro,Sivaniah, Easan,Horike, Satoshi
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p. 5111 - 5114
(2020/05/26)
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- A comparative study on the catalytic activity of ZnAl, NiAl, and CoAl mixed oxides derived from LDH obtained by mechanochemical method in the synthesis of 2-methylpyrazine
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Mixed oxides (mo)-ZnAl; NiAl; CoAl (M2+/Al = 3 M ratio) were obtained from layered double hydroxides (LDH) precursors synthesized by mechanochemical method. The solids were characterized by XRD, DRIFT, H2-TPR, NH3/CO2-TPD and determination of textural properties by N2 adsorption-desorption isotherms. The catalytic activity was tested in the dehydration-cyclization of ethylenediamine with propylene glycol, followed by the dehydrogenation of the obtained piperazine, yielding the 2-methylpyrazine (2-MP) as the main reaction product. At 400 °C, the conversion of both reactants was quasi-total, but the yield to 2-MP was close to 90% on the solids with more active sites favoring dehydration-cyclization (mo-ZnAl and mo-CoAl).
- Teodorescu,Slabu,Pavel,Z?voianu
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- Reactivity of platinum(II) triphenylphosphino complexes with nitrogen donor divergent ligands
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Dinuclear platinum(II) complexes [{PtCl2(PPh3)}2(μ-N–N)], where N–N is a divergent bidentate nitrogen ligand, were prepared by reacting cis-[PtCl2(PPh3)(NCMe)] with N–N in a Pt/N–N molar ratio 2. The (trans,trans)-isomers were obtained as kinetic products and recovered in good yields and high purity {1, N–N?=?pyrazine (pyrz); 2, N–N?=?4,4′-bipyridyl (bipy); 3, N–N?=?piperazine (pipz); 4, N–N?=?p-xylylendiamine (xylN2)}. Cis-[PtCl2(PPh3)(NCMe)] was also reacted with the tridentate divergent ligand 2,4,6-tris-(pyrid-4′-yl)1,3,5-triazine (py3TRIA) in molar ratio 3 with formation of the trinuclear (trans,trans,trans)-[{PtCl2(PPh3)}3(μ-py3TRIA)], 5. On the other hand, the treatment of cis-[PtCl2(PPh3)(NCMe)] with the monodentate pyridine (py) produced a mixture of both trans-[PtCl2(PPh3)(py)] (6a) and cis-[PtCl2(PPh3)(py)] (6b). The reactions of cis-[PtCl2(PPh3)(NCMe)] with N–N?=?pyrz, bipy, pipz, carried out with a Pt/N–N molar ratio 1, were monitored by31P NMR spectroscopy. Equilibria were observed in solution, involving dinuclear (trans–trans)-[{PtCl2(PPh3)}2(μ-N–N)], mononuclear [PtCl2(PPh3)(N–N)] and free N–N. The addition of an excess of the divergent ligand allowed the complete conversion to the corresponding mononuclear complexes. With the heteroaromatic ligands both geometric isomers were observed (7a, 7b and 8a, 8b, for pyrz and bipy derivatives, respectively) while with pipz the trans-isomer only was detected, 9. In the system involving bipy, the scarcely soluble dinuclear (cis,cis)-[{PtCl2(PPh3)}2(μ-bipy)], 2b, was also obtained. Products 2, 2b, 3·2(CHCl3) and 6a·0.5(C2H4?Cl2) were structurally characterized by single crystal X-ray diffraction methods.
- Belli Dell’ Amico, Daniela,Bellucci, Luca,Labella, Luca,Marchetti, Fabio,Samaritani, Simona
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p. 403 - 411
(2016/10/14)
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- The effects of thermal treatment of ZnO–ZnCr2O4 catalyst on the particle size and product selectivity in dehydrocyclization of crude glycerol and ethylenediamine
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The ZnO–ZnCr2O4 (Zn–Cr–O) sample obtained by decomposition of Zn-Cr hydrotalcite precursor was subjected to the thermal treatment at different temperatures and the physico-chemical properties of the Zn–Cr–O system were compared with
- Sarkari, Reema,Krishna, Vankudoth,Sudhakar, Medak,Rao, Tumula Venkateshwar,Padmasri, Aytam Hari,Srinivas, Darbha,Venugopal, Akula
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p. 602 - 609
(2016/10/18)
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- Cyclization of monoethanolamine to aziridine over Cs2O-P 2O5/SiO2
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Several commercially available supports were examined for cyclization of monoethanolamine to aziridine, and SiO2 was found to yield the best results. The obtained results indicated that selectivity of aziridine was mainly influenced by support. The catalysts were characterized by NH3-TPD and XRD. It was found that SiO2 with lower acidity could inhibit the intermolecular condensations, and thus favored the formation of aziridine. The Cs4P2O7 phase was confirmed as the active site in the supported cesium phosphate catalyst. The reaction parameters were also optimized and a yield of 52% aziridine was obtained over 200 h. Thus, a continuous process for the cyclization of monoethanolamine to aziridine has been established. Springer Science+Business Media B.V. 2012.
- Kong, Xiangjin,Wang, Guangyuan,Li, Lei,Sun, Meng,Du, Xiaobao,Chen, Ligong
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p. 1743 - 1750
(2013/02/22)
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- Glycerol catalytic cyclocondensation with ethanediamine to pyrazinyl compounds over the modified SiO2-Al2O3
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The Fe, Zn, and Mn-modified SiO2-Al2O3 catalysts for the glycerol vapor-phase cyclocondensation with ethanediamine (ED) to 2-pyrazinemethanol (2-PMol) and 2-methylpyrazine (2-MP) in a fixed-bed system were prepared by coprecipitation and characterized by N2 adsorption-desorption, X-ray powder diffraction, and NH3 temperature-programmed desorption (NH3-TPD) in the present work. The results showed that the Mn-modified SiO2-Al2O3 catalyst with a SiO2/Al2O3 molar ratio 15.84 and 6% Mn gave the highest catalytic activity for formation of 2-PMol (53.1%) and 2-MP (42.9%). Mn species could cause the modulation of the acidic species of catalysts, improving the glycerol cyclocondensation with ED to 2-PMol, and also acted as the catalytic centers for the hydrodehydration of 2-PMol to 2-MP. However, too many strong acidic sites could lead to ED self-cyclocondensation to form a by-product pyrazine. The optimum temperature was tested to be 380°C for the cyclocondensation over a 6%Mn-SiO2-Al2O 3 catalyst.
- Liu, Chuanqi,Xu, Chenghua,Xia, Tongwei,Guo, Yan,Liu, Jianying
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experimental part
p. 377 - 382
(2012/10/18)
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- Impact of the N-terminal amino acid on the formation of pyrazines from peptides in maillard model systems
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Only a minor part of Maillard reaction studies in the literature focused on the reaction between carbohydrates and peptides. Therefore, in continuation of a previous study in which the influence of the peptide C-terminal amino acid was investigated, this study focused on the influence of the peptide N-terminal amino acid on the production of pyrazines in model reactions of glucose, methylglyoxal, or glyoxal. Nine different dipeptides and three tripeptides were selected. It was shown that the structure of the N-terminal amino acid is determinative for the overall pyrazine production. Especially, the production of 2,5(6)-dimethylpyrazine and trimethylpyrazine was low in the case of proline, valine, or leucine at the N-terminus, whereas it was very high for glycine, alanine, or serine. In contrast to the alkyl-substituted pyrazines, unsubstituted pyrazine was always produced more in the case of experiments with free amino acids. It is clear that different mechanisms must be responsible for this observation. This study clearly illustrates the capability of peptides to produce flavor compounds such as pyrazines.
- Van Lancker, Fien,Adams, An,De Kimpe, Norbert
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scheme or table
p. 4697 - 4708
(2012/08/27)
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- Supramolecular metathesis: Co-former exchange in co-crystals of pyrazine with (R,R)-, (S,S)-, (R,S)- and (S,S/R,R)-tartaric acid
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Co-crystals of dextro-(R,R), levo-(S,S), meso-(R,S) and racemic (R,R-S,S)-tartaric acid with pyrazine were obtained by manual kneading and slurry experiments; subsequent reactions in the solid state between these co-crystals and the various forms of tartaric acid in the solid state and via slurry show that co-former exchange takes place according to the sequence of stability [(R,S)-ta]2·py > (S,S/R,R)-ta·py > (R,R)-ta·py or (S,S)-ta·py.
- Braga, Dario,Grepioni, Fabrizia,Lampronti, Giulio I.
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body text
p. 3122 - 3124
(2012/02/15)
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- Vapor phase synthesis of methylpyrazine using aqueous glycerol and ethylenediamine over ZnCr2O4 catalyst: Elucidation of reaction mechanism
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A novel method has been developed for the synthesis of methylpyrazine (MP) by using aqueous glycerol and ethylenediamine (EDA) over Zn-Cr catalyst derived from hydrotalcite precursors. The X-ray diffraction analysis of the oven-dried Zn-Cr samples synthesized at various pH ranging from 7 to 11 showed hydrotalcite phase whereas the calcined catalysts displayed ZnO and ZnCr2O 4 phases. The cyclisation activity of Zn-Cr catalyst prepared at pH ～ 9 demonstrated 99.4% conversion of EDA and 94% of glycerol with ～ 72% selectivity to MP at a reaction temperature of 400 °C. This process demonstrates direct utilization of bio-glycerol for the synthesis of MP.
- Sarkari, Reema,Anjaneyulu, Chatla,Krishna, Vankudoth,Kishore, Ramineni,Sudhakar, Medak,Venugopal, Akula
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experimental part
p. 1067 - 1070
(2012/01/15)
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- Tuning the surface composition of novel metal vanadates and its effect on the catalytic performance
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Tuning the surface composition of metal vanadates using different cations leads to the development of a new class of highly effective catalysts tested in the ammoxidation of 2-methylpyrazine. Especially, an enrichment of V in the near-surface region is beneficial for improved selectivity. With this approach, a knowledge based optimisation of the catalysts was possible for the first time, which indeed led to highly efficient novel LaVOx catalysts with a high yield of 2-cyanopyrazine (≥85%) and extremely high space-time-yields (ca. 525 g-1CP kg-1cat h-1).
- Dhachapally, Naresh,Kalevaru, V. Narayana,Radnik, Joerg,Martin, Andreas
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body text
p. 8394 - 8396
(2011/09/12)
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- Catalytic synthesis of 2-methylpyrazine over Cr-promoted copper based catalyst via a cyclo-dehydrogenation reaction route
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The cyclo-dehydrogenation of ethylene diamine and propylene glycol to 2-methylpyrazine was performed under the atmospheric conditions at 380°C. The Cr-promoted Cu-Zn/Al 2O 3 catalysts were prepared by impregnation method and characterized by ICP-AES, N 2 adsorption/desorption, XRD, XPS, N 2O chemisorption, TPR and NH3-TPD techniques. The amorphous chromium species existing in Cu-Zn-Cr/Al 2O 3 catalyst enhanced the dispersion of active component Cu, promoted the reduction of catalyst. Furthermore, the catalytic performance was significantly improved. The acidity of the catalyst played an important role in increasing the 2-MP selectivity. To optimize the reaction parameters, influences of different chromium content, reaction temperature, liquid hourly space velocity (LHSV), reactants molar ratio and time on stream on the product pattern were studied. The results demonstrated that addition of chromium promoter revealed satisfying catalytic activity, stability and selectivity of 2-methylpyrazine. Indian Academy of Sciences.
- Jing, Fangli,Zhang, Yuanyuan,Luo, Shizhong,Chu, Wei,Zhang, Hui,Shi, Xinyu
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scheme or table
p. 621 - 630
(2010/12/25)
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- Formation of pyrazines in maillard model systems of lysine-containing dipeptides
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Whereas most studies concerning the Maillard reaction have focused on free amino acids, little information is available on the impact of peptides and proteins on this important reaction in food chemistry. Therefore, the formation of flavor compounds from the model reactions of glucose, methylglyoxal, or glyoxal with eight dipeptides with lysine at the N-terminus was studied in comparison with the corresponding free amino acids by means of stir bar sorptive extraction (SBSE) followed by GC-MS analysis. The reaction mixtures of the dipeptides containing glucose, methylglyoxal, and glyoxal produced 27, 18, and 2 different pyrazines, respectively. Generally, the pyrazines were produced more in the case of dipeptides as compared to free amino acids. For reactions with glucose and methylglyoxal, this difference was mainly caused by the large amounts of 2,5(6)-dimethylpyrazine and trimethylpyrazine produced from the reactions with dipeptides. For reactions with glyoxal, the difference in pyrazine production was rather small and mostly unsubstituted pyrazine was formed. A reaction mechanism for pyrazine formation from dipeptides was proposed and evaluated. This study clearly illustrates the capability of peptides to produce flavor compounds that can differ from those obtained from the corresponding reactions with free amino acids.
- Van Lancker, Fien,Adams,De Kimpe, Norbert
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scheme or table
p. 2470 - 2478
(2010/09/04)
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- Intermolecular condensation of ethylenediamine to 1,4-diazabicyclo[2,2,2]octane over TS-1 catalysts
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The intermolecular condensation of ethylenediamine (EDA) to 1,4-diazabicyclo[2.2.2]octane or triethylenediamine (TEDA) has been carried out over various titanosilicate catalysts. Superior to Ti-MWW, Ti-Beta, Ti-FER, and Ti-MOR, TS-1 showed higher EDA conversion and TEDA selectivity. The effects of reaction parameters, Ti content, and crystal size on the EDA condensation over TS-1 have been investigated. The mechanism for the TS-1-catalyzed condensation of EDA has also been considered. The acid sites, originated from the Si-OH groups adjacent to the "open" Ti sites, were assumed to contribute to the intermolecular condensation of EDA, whereas the Lewis acid sites directly related to Ti(IV) ions were not the true active sites. The primary intermolecular condensation of EDA to 1,4-diazacyclohexane or piperazine (PIP) took place mainly inside the micropores of the MFI structure, while the secondary condensation of PIP with EDA to TEDA was favored by the acid sites located near the pore entrance and on the outer surface of crystals.
- Wang, Yong,Liu, Yueming,Li, Xiaohong,Wu, Haihong,He, Mingyuan,Wu, Peng
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experimental part
p. 258 - 267
(2011/03/17)
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- Magnesium borohydride confined in a metal-organic framework: A preorganized system for facile arene hydroboration
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(Chemical Equation Presented) In close quarters: When confined in a metal-organic framework, magnesium borohydride reacts with arenes by a hydroboration pathway (see scheme), in contrast to its reactivity under analogous homogeneous solution-phase conditi
- Ingleson, Michael J.,Barrio, Jorge Perez,Bacsa, John,Steiner, Alexander,Darling, George R.,Jones, James T. A.,Khimyak, Yaroslav Z.,Rosseinsky, Matthew J.
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supporting information; body text
p. 2012 - 2016
(2009/07/25)
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- One-Pot Two-Step Synthesis of Aryl Sulfur Compounds by Photoinduced Reactions of Thiourea Anion with Aryl Halides
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(Equation presented) The photoinduced reactions of aryl halides with the thiourea anion afford arene thiolate ions in DMSO. These species without isolation, and by a subsequent aliphatic nucleophilic substitution, S RN1 reaction, oxidation, or protonation, yield aryl methyl sulfides, diaryl sulfides, diaryl disulfides, and aryl thiols with good yields (50-80%). This is a simple and convenient approach which involves the use of the commercially available and inexpensive thiourea in a one-pot two-step process for the synthesis of aromatic sulfur compounds.
- Argueello, Juan E.,Schmidt, Luciana C.,Penenory, Alicia B.
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p. 4133 - 4136
(2007/10/03)
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- Pyrazine formation from serine and threonine
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The formation of pyrazines from L-serine and L-threonine has been studied. L-Serine and L-threonine, either alone or combined, were heated at 120 °C as low temperature for 4 h or at 300 °C as high temperature for 7 min. The pyrazines formed from each reaction were identified by GC/MS, and the yields (to the amino acid used, as parts per million) were determined by GC/FID. It was found that pyrazine, methylpyrazine, ethylpyrazine, 2-ethyl-6- methylpyrazine, and 2,6-diethylpyrazine were formed from serine, whereas 2,5- dimethylpyrazine, 2,6-dimethylpyrazine, trimethylpyrazine, 2-ethyl-3,6- dimethylpyrazine, and 2-ethyl-3,5-dimethylpyrazine were formed from threonine. Mechanistically, it is proposed that the thermal degradation of serine or threonine is composed of various complex reactions. Among these reactions, decarbonylation followed by dehydration is the main pathway to generate the α-aminocarbonyl intermediates leading to the formation of the main product, such as pyrazine from serine or 2,5-dimethylpyrazine from threonine. Also, deamination after decarbonylation generates more reactive intermediates, α-hydroxycarbonyls. Furthermore, aldol condensation of these reactive intermediates provides α-dicarbonyls. Subsequently, these α- dicarbonyls react with the remaining serine or threonine by Strecker degradation to form additional α-aminocarbonyl intermediates, which then form additional pyrazines. In addition, decarboxylation and retroaldol reaction may also involve the generation of the intermediates.
- Shu, Chi-Kuen
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p. 4332 - 4335
(2007/10/03)
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- Degradation Products Fromed from Glucosamine in Water
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An aqueous solution of glucosamine hydrochloride was heated to 150 °C for 5 min under different pH conditions. The reaction product mixture obtained was analyzed by GC/MS. It was found that the major products formed were furfurals, especially at pH = 4 and 7. At pH = 8.5, additional flavor components were generated, including pyrazines, 3-hydroxypyridines, pyrrole-2-carboxaldehyde, furans, acetol, and several other compounds. Of the components identified, it is worthwhile to note the formation of pyrazine and methylpyrazine as major components at pH = 8.5. It is proposed that a retro-aldol condensation plays an important role in the formation of the intermediates, α-aminoacetaldehyde (I) and α-amino propanal (II). As a result, self-condensation of I generates pyrazine and combination of I and II generates methylpyrazine. In addition, it is also interesting to note the formation of 3-hydroxypyridines and pyrrole-2-carboxaldehyde. It is suggested that both groups of compounds are derived from furfurals. As the ammonia is liberated from glucosamine, it initiates the ring-opening of furfurals to form 5-amino-2-keto-3-pentenals. Intramolecular condensations of these intermediates between the amino group and the carbonyl groups lead to the formation of 3-hydroxypyridines and pyrrole-2-carboxalhyde.
- Shu, Chi-Kuen
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p. 1129 - 1131
(2007/10/03)
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- Volatile Compounds Generated from Thermal Reaction of Methionine and Methionine Sulfoxide with or without Glucose
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Methionine and methionine sulfoxide were mixed with or without glucose in distilled water, individually.These solutions were heated in closed sample cylinders at 180 deg C for 1 h.The volatile compounds generated were extracted using methylene chloride and analyzed by GC and GC-MS.Pyrazine compounds, especially 2,5-dimethyl-, 2-ethyl-5-methyl-, trimethyl-, and methylpyrazines were the predominant compounds among those generated from thermal interactions of glucose and methionine or methionine sulfoxide.The formation of methional or those compounds derived for methional was found to be more favorable from the thermal degradation of methionine, whereas the formation of dimethyl polysulfides, especially dimethyl disulfide and dimethyl trisulfide, was found to be more favorable from the thermal degradation of methionine sulfoxide.Glucose was found to have a catalytic effect on the formation of volatile compounds from the thermal degradation of methionine or methionine sulfoxide.Keywords: Methionine; methionine sulfoxide; methional; methyl sulfides; volatiles
- Yu, Tung-Hsi,Ho, Chi-Tang
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p. 1641 - 1646
(2007/10/02)
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- Substituted pyrazines
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The present invention provides novel substituted pyrazines or pyrazine derivatives ("NPD") which are functional and have useful application as a monomer for a variety of high performance polymers such as polyester, polyarylate, polycarbonate, polyetherketones, epoxides, polyimides, polyamides, and polyamides-imides. These NPD have the general formula: STR1 wherein R1, R2, R3, and R4 are defined herein.
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- Biphenyl pyrazine compounds
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The present invention provides novel substituted biphenyl pyrazines or pyrazine derivatives ("BPD") which are functional and have useful application as a monomer for a variety of high performance polymers such as polyester, polyarylate, polycarbonate, polyetherketones, epoxides, polyimides, polyamides, and polyamides-imides; and as pigments for coating compositions such as paints. These BPD have the formula: STR1
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- SYNTHESIS OF NITROGEN CONTAINING HETEROCYCLES OVER COPPER CHROMITE
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The reactions of 1,2-diaminopropane, 1-amino-2-propanol, 1-amino-2-ethanol, and N-(β-aminoethyl)-1,2-diaminoethane in the gas phase over copper chromite have been investigated with the objective of synthesising nitrogen containing heterocycles.At 240-360
- Meksh, P.A.,Anderson, A.A.,Shimanska, M.
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p. 822 - 828
(2007/10/02)
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- Pt/Al2O3 CATALYSTS IN THE SYNTHESIS OF NITROGEN HETEROCYCLES. CATALYTIC SYNTHESIS OF PYRAZINES
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A study was carried out on the use of Pt/Al2O3 catalysts in the synthesis of pyrazines via the dehydrogenation of piperazines, dehydrodeamination of diamines, and dehydrocyclocondensation of N-hydroxyalkyldiamines.In contrast to the current hypothesis of the intermediate formation of piperazine in the latter two reactions, evidence was found that these reactions proceed through initial dehydrogenation and the dehydrogenated intermediate then undergoes cyclization.Polyalkylpyrazines, formed by the alkylation of the pyrazine ring by hydrogenolysis products, are the major side-products in all the reactions studied.Pyrazines may be obtained in high yield and satisfactory selectivity by selecting suitable modifiers, which enhance the dehydrogenation activity of the catalyst and suppress the hydrogenolysis of the C-N bond.
- Gitis, K. M.,Neumoeva, G. E.,Isagulyants, G. V.
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p. 1308 - 1315
(2007/10/02)
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- Catalytic Synthesis Of Aziridine From 1,2-Diaminoethane
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The contact conversion of 1,2-diaminoethane over a tungsten trioxide catalyst at 240-580 deg C has been studied by an impulse chromatographic method.The basic reaction path under these conditions is unimolecular deaminocyclization to give aziridine (31-35percent).Piperazine and triethylenediamine, products of bi- and trimolecular deaminocyclization, are present as products.The deamination process is accompanied by coupled dehydrogenation and hydrogenolysis reactions.Addition of the acid anhydrides SiO2, P2O5 and B2O3 to the catalyst increases its activity but has onlyanegligible affect on the activation energy of the process.
- Anderson, A. A.,Simonyan, S. P.,Shimanskaya, M. V.
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p. 1134 - 1141
(2007/10/02)
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- Intermolecular and intramolecular cyclization over modified ZSM-5 and chromite catalysts to synthesize 2-methyl pyrazine and piperazine
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The synthesis of methyl pyrazine and piperazine has been carried out over HZSM-5 and modified copper-chromite catalysts.The reaction occurs through the dehydrocyclization route at acidic centres.The Bronsted acidic centres at interstitial are particularly responsible for the conversion of propylene glycol, propylene oxide with ethylenediamine and β-hydroxy-propylethylenediamine to the N-containing heterocycles through intermolecular and intramolecular cyclization.In the formation of N-containing heterocycles, the steps involved are dehydration and cyclization.The important difference between these reactions and the methano-to-gasoline (MTG) process is the formation of olefinic compounds as intermediates in the latter.
- Kulkarni, S. J.,Subrahmanyam, M.,Rao, A. V. Rama
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- EFFECT OF TIME AND TEMPERATURE ON THE PREPARATION OF PYRAZINES IN MODEL REACTIONS OF THE SYNTHESIS OF AROMA-FORMING SUBSTANCES
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The qualitative and quantitative compositions of pyrazines that form in model glucose-ammonia and glucose-ammonia-leucine reactions in a glycerol medium were studied.Reaction conditions were found that ensure the synthesis of 23 alkylpyrazines in total concentration ca. 6 g/kg.The obtained mixture of pyrazines is promising for use in the development of food aroma-forming substances.Keywords: pyrazines, Maillard reaction, capillary gas chromatography.
- Misharina, T. A.,Golovnya, R. V.,Yakovleva, V. N.
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p. 1258 - 1263
(2007/10/02)
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- DEHYDROGENATION OF PIPERAZINE INTO PYRAZINE ON ALUMINA-PLATINUM CATALYSTS
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Dehydrogenation of piperazine on alumina-platinum catalysts at 360-400 deg C was investigated.It was found that the alumina-platinum catalyst has low selectivity in the formation of pyrazine (yield /= 43percent), and dehydrogenation is accompanied by decomposition and coke formation and products of decomposition in the formation of alkylpyrazines.The alumina-platinum catalyst in In2O3 and Re2O7 additives permits obtaining pyrazine with a yield of up to 80percent.Dehydrogenation of piperazine is accompanied by reactions of decomposition, dehydroisomerization, and alkylation to a small degree, resulting in the formation of pyrrole, methylimidazole, and alkylpyrazines.
- Isagulyants, G. V.,Gitis, K. M.,Myasnikov, V. A.,Neumoeva, G. E.
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p. 1340 - 1345
(2007/10/02)
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- An N.M.R. Study of Electron Donor-Electron Acceptor Interaction Between Aromatic Hydrocarbons and Diazines
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Equilibrium constants have been measured by n.m.r. spectroscopy for the electron donor-electron acceptor interaction between a number of aromatic hydrocarbons and diazines.The values obtained have shown that the interaction is weak, and that the aromatic hydrocarbon acts as the electron donor and the diazine as the electron acceptor in the systems studied.Chemical-shift data have provided evidence for the relative positioning of the donor and acceptor components within the various complexes.The effect of temperature on the equilibrium constant for complex formation between (2H6)benzene and pyrazine has shown that the enthalpy of format ion is close to zero.
- Hurst, Derek T.,Thakrar, Usha B.,Wells, Clifford H. J.,Wyer, John
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p. 1313 - 1319
(2007/10/02)
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- Crystal Growth in Gels and X-Ray Characterization of Polymeric 1:1 Complexes of CuBr2 and CuCl2 with Pyrazine
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Single crystals of Cu(pz)Br2 and Cu(pz)Cl2, were grown by using gel methods with tetramethoxysilane as the gel-forming reagent.Thermal decomposition is interpreted.Crystal data for the bromo complex: monoclinic, space group C2/m with a = 1239.2(3) pm, b = 685.9(2) pm, c = 390.7(3) pm, β = 96.23(5) deg.Crystal data for the chloro-complex: monoclinic, space group C2/m with a = 1197.1(3) pm, b = 684.9(3) pm, c = 370.1(3) pm, β = 95.96(5) deg.Crystal structure analyses reveal that CuHal2 molecules are bonded by pyrazine to form linear chains.These chains are cross-linked by bridging halogen atoms. - Keywords: Pyrazine, Copper Complexes, Polymeric Complexes, Gel Crystallization
- Fetzer, Th.,Lentz, A.,Debaerdemaeker, T.
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p. 553 - 556
(2007/10/02)
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