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PubMed2003

Synthesis of naturally occurring acetylenes via an alkylidene carbenoid rearrangement.

Naturally occurring mosquito larvicidal acetylenes 1 and 2, and analogues 3 and 4, each containing either a 1,3-butadiynyl or a 1,3,5-hexatriynyl moiety, are synthesized via a Fritsch-Buttenberg-Wiechell rearrangement. The alkylidene carbenoid intermediate results from lithium-halogen exchange of a suitable dibromoolefin precursor, and the rearrangement is accomplished under mild conditions. Synthesis of the dibromoolefin precursors to acetylenes 1-4 is easily achieved in three steps from commercially available carboxylic acids or aldehydes, making this procedure a viable alternative to conventional methods for the synthesis of naturally occurring acetylenes.

Acetylene↗
PubMed2001

Synthesis of diynes and tetraynes from in situ desilylation/dimerization of acetylenes.

[reaction: see text]. An efficient method for the in situ desilylation/oxidative dimerization of (trialkylsilyl)acetylenes is described. This protocol avoids the complications encountered with sensitive diynes by eliminating the deprotection and isolation steps. Various aromatic and alkyl diynes and tetraynes can be synthesized in a straightforward manner in good yields (82-99%) from TIPS-protected acetylenes. This method facilitates the efficient synthesis of novel tetrayne-bridged acetylenic cyclophanes 6 and 7 in a direct manner.

Acetylene↗
PubMed1978

Electron-paramagnetic-resonance studies on nitrogenase of Klebsiella pneumoniae. Evidence for acetylene- and ethylene-nitrogenase transient complexes.

Klebsiella pneumoniae nitrogenase exhibited four new electron-paramagnetic-resonance signals during turnover at 10 degrees C, pH7.4, which were assigned to intermediates present in low concentrations in the steady state. 57Fe-substituted Mo--Fe protein showed that they arose from Fe--S clusters in the Mo--Fe protein of nitrogenase. The new signals are designated: Ic, g values at 4.67, 3.37 and approx. 2.0; VI, g values at 2.125, 2.000 and 2.000; VII, g values at 5.7 and 5.4; VIII, g values at 2.092, 1.974 and 1.933. The sharp axial signal VI arises from a Fe4S4 cluster at the --1 oxidation level. This signal was only detected in the presence of ethylene and provides the first evidence of an enzyme--product complex for nitrogenase. [13C]Acetylene and [13C]ethylene provided no evidence for direct binding of this substrate and product to the Fe--S clusters giving rise to these signals. The dependence of signal intensities on acetylene concentration indicated two types of binding site, with apparent dissociation constants K less than 16 micron and K approximately 13mM. A single binding site for ethylene (K=1.5mM) was detected. A scheme is proposed for the mechanism of reduction of acetylene to ethylene and inhibition of this reaction by CO.

Acetylene↗
PubMed1981

An investigation of 11C-methane, 13N-nitrous oxide and 11C-acetylene as regional cerebral blood flow agents.

Radioisotopes of xenon or krypton are generally used as the inert diffusible indicators in regional cerebral blood flow (rCBF) studies. These gases have disadvantages when introduced into the body inhalation because of their low solubility in body tissues. The use of 11C-methane, 13N-nitrous oxide and 11C-acetylene as inhalation rCBF agents has been investigated. These gases span a wide range of solubilities: methane is four times less soluble than xenon in body tissues while nitrous oxide and acetylene are respectively 3 and 6 times more soluble. Cerebral blood flow measurements were performed on normal volunteers using the three labelled gases as well as 133Xe. All tracers were administered by inhalation and the cerebral clearance of the gases was monitored by coincidence detection. Uptake in the body was found to be dependent on solubility. The computed blood flow values found using the various indicators were in excellent agreement and were within the normal cerebral blood flow range. The high solubilities of acetylene and nitrous oxide result in a more efficient transfer of tracer from lung to brain than the conventionally used agents. The positron emission is also advantageous for tomographic rCBF measurements.

Acetylene↗
PubMed1978

Biological dinitrogen fixation (acetylene reduction) associated with Florida mangroves.

Biological dinitrogen fixation in mangrove communities of the Tampa Bay region of South Florida was investigated using the acetylene reduction technique. Low rates of acetylene reduction (0.01 to 1.84 nmol of C(2)H(4)/g [wet weight] per h) were associated with plant-free sediments, while plant-associated sediments gave rise to slightly higher rates. Activity in sediments increased greatly upon the addition of various carbon sources, indicating an energy limitation for nitrogenase (C(2)H(2)) activity. In situ determinations of dinitrogen fixation in sediments also indicated low rates and exhibited a similar response to glucose amendment. Litter from the green macroalga, Ulva spp., mangrove leaves, and sea grass also gave rise to significant rates of acetylene reduction. Higher rates of nitrogenase activity (15 to 53 nmol of C(2)H(4)/g [wet weight] per h were associated with washed excised roots of three Florida mangrove species [Rhizophora mangle L., Avicennia germinans (L) Stern, and Laguncularia racemosa Gaertn.] as well as with isolated root systems of intact plants (11 to 58 mug of N/g [dry weight] per h). Following a short lag period, root-associated activity was linear and did not exhibit a marked response to glucose amendment. It appears that dinitrogen-fixing bacteria in the mangrove rhizoplane are able to use root exudates and/or sloughed cell debris as energy sources for dinitrogen fixation.

Acetylene↗
PubMed1992

Inhibition of alkylbenzene biodegradation under denitrifying conditions by using the acetylene block technique.

Addition of acetylene to microcosms simultaneously amended with nitrate and alkylbenzenes resulted in inhibition of the rate of alkylbenzene biodegradation under denitrifying conditions. Toluene, xylenes, and 1,2,4-trimethylbenzene were recalcitrant, whereas ethylbenzene was degraded at a slower rate than usual. Benzene was not degraded in either case. Addition of acetylene to microcosms preexposed to nitrate and alkylbenzenes produced similar inhibition. These data indicate that the activities of microorganisms that degrade alkylbenzenes under denitrifying conditions may be suppressed if the standard acetylene block technique is used to verify denitrifying activity.

Acetylene↗
PubMed1981

Nitrogen fixation (acetylene reduction) by Klebsiella pneumoniae in association with 'Park' Kentucky bluegrass (Poa pratensis L.).

Turks of 'Park' Kentucky bluegrass reestablished in the greenhouse and inoculated with Klebsiella pneumoniae (W6) showed significantly increased nitrogen fixation (acetylene reduction) compared with control turfs. Mean ethylene production rates per pot were 368 nmol h-1 for K. pneumoniae treated turfs, 55 nmol h-1 for heat-killed K. pneumoniae treated turfs, and 44 nmol h-1 for untreated turfs. Calculated lag periods before activity was observed were generally very short (less than 1 h). When 'Park' Kentucky bluegrass was grown from seed on soil-less medium of Turface, a fired aggregate clay, inoculation with K. pneumoniae (W6) resulted in 9 of 11 turfs showing nitrogenase activity (mean ethylene production rate per pot was 195 nmol h-1). Only 3 of 11 turfs treated with heat-killed K. pneumoniae showed any activity and their mean rate of ethylene production (40 nmol h-1 per pot) was significantly lower than that for turfs treated with K. pneumoniae. Using the 'Park'--Turface soil-less model system it was shown that acetylene reducing activity was (i) root associated, (ii) generally highest at a depth of 1--4 cm below the surface, (iii) enhanced by washing excised roots, and (iv) inhibited by surface sterilization of excised roots. Klebsiella pneumoniae was recovered from Turface and roots showing acetylene reducing activity.

Acetylene↗
PubMed1985

Effect of O2 on vesicle formation, acetylene reduction, and O2-uptake kinetics in Frankia sp. HFPCcI3 isolated from Casuarina cunninghamiana.

The effect of the partial pressure of oxygen (PO2) on the formation of vesicles, which are thought to be the site of N2 fixation in Frankia, was studied in HFPCcI3, an effective isolate from Casuarina cunninghamiana. Unlike other actinorhizal root nodules, vesicles are not produced by the endophyte in Casuarina nodules. However, in culture under aerobic conditions, large, phase-bright vesicles are formed in HFPCcI3 within 20 h following removal of NH+4 from the culture medium and reach peak numbers within 72 to 96 h. In vivo acetylene reduction activity parallels vesicle formation. Optimum rates of acetylene reduction in short-term assays occurred at 20% O2 (0.2 atm (1 atm = 101.325 kPa] in the gas phase. O2 uptake (respiration) determined polarographically showed diffusion-limited kinetics and remained unsaturated by O2 until 300 microM O2. In contrast, respiration in NH+4-grown cells was saturated by O2 between 8 and 10 microM O2. These results indicate the presence of a diffusion barrier associated with the vesicles. Vesicle development was repressed in cells incubated in N-free media sparged with gas mixtures with PO2 between 0.001 and 0.003 atm. Nitrogenase was induced under these conditions, but acetylene reduction was extremely O2 sensitive. The kinetics of O2 uptake as a function of dissolved O2 concentration in avesicular cells were similar to those in NH+4-grown cells indicating the lack of a diffusion barrier. These results demonstrate that vesicle formation and the development of the O2 protection mechanisms of nitrogenase are regulated by ambient PO2 in HFPCcI3.

Acetylene↗
PubMed2002

High yield of pure multiwalled carbon nanotubes from the catalytic decomposition of acetylene on in-situ formed cobalt nanoparticles.

For the first time, multiwalled carbon nanotubes (MWNTs) could be formed selectively in a high yield, free of any disordered carbon by-product, from the catalytic decomposition of acetylene at 600 degrees C on a CoxMg(1-x)O solid solution. Starting from 1 g of catalytic substrate, 4 g of pure MWNTs were obtained after its dissolution in boiling concentrated HCl, without any additional purification in strongly oxidizing medium, as is required for other methods of nanotube production. In situ reduction of CoO by dihydrogen liberated from acetylene decomposition allows highly divided metal particles to be continuously produced as synthesis proceeds. This is undoubtedly the reason for the good performance of the catalyst and for the ability to produce nanotubes in a narrow diameter range, namely from 10 to 15 nm. With the use of acetylene instead of methane, the synthesis proceeds at low temperature, which prevents the growth of carbon shells, in which the metal particles are generally embedded, decreasing their activity. Because of the very low specific surface area of the catalyst support, the amount of disordered carbon by-product formed is negligible.

Acetylene↗
PubMed2000

[A case of acute eosinophilic pneumonia induced by inhalation of acetylene].

A 17-year-old high school student, while carrying out soldering one morning, inhaled 100% acetylene, and experienced nausea and bilateral lower limb numbness several hours later. In the evening his symptoms worsened, dyspnea followed, and the patient was referred to our hospital the next day. On admission chest radiography and CT scanning revealed peripheral ground-glass opacity, patchy infiltrate and Kerley's B line in the right lung fields, and bilateral pleural effusion. Since the laboratory findings revealed leukocytosis without eosinophilia, increased CRP, and hypoxemia, bronchoalveolar lavage (BAL) and transbronchial biopsy (TBLB) was subsequently performed. Fluid analysis revealed marked increases in the total cell and eosinophil counts, and the biopsy result showed eosinophilic and lymphocytic infiltration of the alveolar septa. As a result, the case was diagnosed as acute eosinophilic pneumonia (AEP). Although inhalation of acetylene is known to induce pulmonary edema, all the typical findings of AEP but pulmonary edema were seen. This case demonstrates that AEP may be induced by inhalation of acetylene.

Acetylene↗
PubMed2002

[Determination of acetylene and vinyl chloride in hydrochloric acid from producing vinyl chloride by headspace gas chromatography].

A headspace gas chromatographic method was used for determining acetylene and vinyl chloride in hydrochloric acid from vinyl chloride production. Hydrogen chloride was neutralized by sodium hydroxide, so its effect on determining acetylene and vinyl chloride was eliminated. The headspace bottle was put in a water bath at 35 degrees C for 45 min. The GC column was a 2 m x 3 mm i.d. stainless steel tube packed with GDX-202 stationary phase. The column temperature was 140 degrees C. Injection volume was 1 mL. External standard method was used for quantitation. The relative standard deviation was 0.85% and the recoveries in the range of 30.0 micrograms/g-150 micrograms/g were 98.9%-103% for acetylene. The relative standard deviation was 1.4% and the recoveries in the range of 20.0 micrograms/g-100 micrograms/g were 98.8%-102% for vinyl chloride.

Acetylene↗
PubMed1992

[Pulmonary blood flow measurement by acetylene rebreathing method in subjects without respiratory function disturbance].

Simultaneous measurement of pulmonary blood flow by the acetylene rebreathing method and cardiac output by the thermodilution method was performed in subjects without respiratory function disturbance during right heart catheterization. After the measurement of cardiac output, the subjects rebreathing a gas mixture containing acetylene and argon from the end tidal level. The inspiratory and expiratory gases were measured by a mass-spectrometer. Results were analyzed by a lung model consisting of two compartments (rebreathing bag compartment and lung compartment), while taking into account the volume reduction due to O2 and CO2 exchange and the fluctuation of end tidal gas concentration until equilibrium between the bag and the lung. The correlation coefficient between these two methods was 0.944, which was statistically significant. The regression line was near the line of identity. The measurement of pulmonary blood flow by the acetylene rebreathing method was applicable in cases without lung function disturbance.

Acetylene↗
PubMed2005

Accidental death resulting from acetylene cylinder impact.

Acetylene is an inflammable gas commonly used for welding in small-scale industries. We present a case of a 34-year-old male welder who died following injuries sustained from explosion of an acetylene gas-welding cylinder. In this case report, we discuss the circumstances leading to the explosion of the welding cylinder, the autopsy findings, and a brief review of the literature on deaths resulting from blasts of acetylene cylinders.

Accidents, Occupational↗
PubMed1976

Influence of different types of acetylene-oxygen flames on the carbon content of a dental Co-Cr alloy.

The influence of different acetylene-oxygen flames on the carbon content of a dental cobalt-chromium alloy, type A, was studied under standardised casting conditions. The alloy was cast, both immediately after the formation of the Bull's eye and after prolonging the melting time. Further, the effect of re-casting, varying the amount of alloy casted and using different sections of the same acetylene-oxygen flame when melting was studied. The results showed on the one hand that the chemical character of the section of flame used and not the gasmixture as such determined the carbon content of the casting, and on the other that the acetylene-oxygen flames can increase but not decrease the carbon content in the casting. Increase of the carbon content of a cobalt-chromium alloy causes a considerable change in its microstructure.

Acetylene↗
PubMed1997

[Use of acetylene rebreathing to measure pulmonary tissue volume in patients undergoing hemodialysis].

Acetylene rebreathing was used to measure pulmonary tissue volume in 10 normal subjects and in 15 patients undergoing hemodialysis. A mixture containing 0.65% acetylene and 10% argon was rebreathed from the end-tidal level, and gas concentrations were measured with a mass spectrometer. Pulmonary tissue volume was computed from the difference between the argon equilibrium concentration and the corrected acetylene concentration, under the assumption that FAr was constant. Measured tissue volumes per unit lung volume (at functional residual capacity) in the normal subjects, before hemodialysis, and after hemodialysis were 0.204 +/- 0.042, 0.334 +/- 0.100, and 0.282 +/- 0.074, respectively. Tissues volumes per unit lung volume were significantly higher in the patients than in the normal subjects, even after hemodialysis. Tissues volumes per unit of lung volume decreased significantly during hemodialysis. Pulmonary blood flows per unit of body surface area of normal subjects, before hemodialysis and after hemodialysis were 3.004 +/- 0.791, 2.790 +/- 1.007, and 2.399 +/- 0.781 (l/min/m2), respectively. These volumes did not differ significantly between normal subjects and patients, and they decreased significantly during hemodialysis. Measured tissue volumes per unit of pulmonary blood flow for normal subjects, before hemodialysis, and after hemodialysis were 0.119 +/- 0.034, 0.167 +/- 0.024, and 0.166 +/- 0.030 (1/1/min), respectively. The values in the patients did not change during hemodialysis, but they were significantly higher than the volumes in the normal subjects.

Acetylene↗
PubMed2000

Gas-phase reactions of nitronium ions with acetylene and ethylene: an experimental and theoretical study

A comparative study of the gas-phase reactions of NO2+ with acetylene and ethylene was performed by using FT-ICR, MIKE, CAD, and NfR/ CA mass spectrometric techniques, in conjunction with ab initio calculations at the MP2/6-31+G* level of theory. Both reactions proceed according to the same mechanism, that is, 1,3-dipolar cycloaddition, but yield products of different stability. The C2H2NO2+ adduct from acetylene has an aromatic character and hence is highly stabilized with respect to the C2H4NO2+ adduct from ethylene. Both cycloadducts tend to isomerize into O-nitroso derivatives, that is, nitrosated ketene and nitrosated acetaldehyde, which represent the thermodynamically most stable products from the addition of NO2+ to acetylene and ethylene, respectively. As prototypal examples of the reactivity of free nitronium ions with most simple pi systems, the reactions investigated are useful starting points to model the mechanism of aromatic nitration.

Journal Article↗
PubMed2001

Reactivity of calix-tetrapyrrole SmII and SmIII complexes with acetylene: isolation of an "N-confused" calix-tetrapyrrole ring.

The nature of the substituents present on the calix-tetrapyrrole tetra-anion ligand [[R2C(C4H2N)]4]4- (R = [-(CH2)5-]0.5, Et) determines the type of reactivity of the corresponding SmII compounds with acetylene. With R = [-(CH2)5-]0.5, dehydrogenation occurred to yield the nearly colorless dinuclear diacetylide complex [[[[-(CH2)5-]4-calix-tetrapyrrole]SmIII]2(mu-C2Li4)].THF as the only detectable reaction product. Conversely, with R = Et, acetylene coupling in addition to dehydrogenation resulted in the formation of a dimeric butatrienediyl enolate derivative [[(Et8-calix-tetrapyrrole)SmIII[Li[Li(thf)]2(mu-OCH=CH2)]]2(mu,eta2,eta'2-HC=C=C=CH)]. Reaction of the trivalent hydride [(Et8-calix-tetrapyrrole)(thf)SmIII[(mu-H)[Li(thf)]]2 or of the terminally bonded methyl derivative [(Et8-calix-tetrapyrrole)(CH3)SmIII[[Li(thf)]2[Li(thf)2](mu3-Cl)]] with acetylene resulted in a mixture of the carbide [[(Et8-calix-tetrapyrrole)SmIII]2(mu-C2Li4)].Et2O with the dimerization product [[(Et8-calix-tetrapyrrole)SmIII[Li[Li(thf)]2(mu3-OCH=CH2)]]2-mu,eta2,eta'2-HC=C=C=CH)]. The same reaction also yielded a third product, a trivalent complex [[(Et8-calix-tetrapyrrole)SmIII[Li(thf)2]]2], in which the macrocycle was isomerized by shifting the ring attachment of one of the four pyrrole rings.

Journal Article↗