Acetylene determination

Chemical. To check against the possibility of errors either in the sampling procedure or in the value taken for the total volume of gas passed through the arc, the total amount of acetylene produced was estimated by a wet chemical method. The total volume of gas collected in the Polythene bag was used for this analysis. Acetylene determination was made using potassium mercuric iodide, dissolved in potassium iodide, in the presence of sodium hydroxide. 

Example 2.10 Determination of the adiabatic flame temperature of acetylene Determine the adiabatic flame temperature of acetylene for an initial temperature of 25 °C using the following mean values for the heat capacities at constant pressure. The net calorific value of acetylene, C , is taken from Table 2.15. 

The regioselectivity of the reaction appears to be determined by a balance of electronic and steric factors. For acrylate and propiolate esters, the carb-oxylate group is found preferentially at C3 of the carbazole product[6-8]. Interestingly, a 4-methyl substituent seems to reinforce the preference for the EW group to appear at C3 (compare Entries 4 and 5 in Table 16.2). For disubstituted acetylenic dicnophiles, there is a preference for the EW group to be at C2 of the carbazole ring[6]. This is reinforced by additional steric bulk in the other substituent[6,9]. 

Description of Method. Copper and zinc are isolated by digesting tissue samples after extracting any fatty tissue. The concentration of copper and zinc in the supernatant are determined by atomic absorption using an air-acetylene flame. 

M HNO3. The concentration of Cu and Zn in the diluted supernatant is determined by atomic absorption spectroscopy using an air-acetylene flame and external standards. Copper is analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc is analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction is used for zinc. Results are reported as micrograms of Cu or Zn per gram of FFDT. 

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

The preferred quantitative deterrnination of traces of acetylene is gas chromatography, which permits an accurate analysis of quantities much less than 1 ppm. This procedure has been highly developed for air poUution studies (88) (see Airpollution control methods). Other physical methods, such as infrared and mass spectroscopy, have been widely used to determine acetylene in various mixtures. 

Acetylene Derived from Hydrocarbons The analysis of purified hydrocarbon-derived acetylene is primarily concerned with the determination of other unsaturated hydrocarbons and iaert gases. Besides chemical analysis, physical analytical methods are employed such as gas chromatography, ir, uv, and mass spectroscopy. In iadustrial practice, gas chromatography is the most widely used tool for the analysis of acetylene. Satisfactory separation of acetylene from its impurities can be achieved usiag 50—80 mesh Porapak N programmed from 50—100°C at 4°C per minute. 

To extend the study of the apparent decomposition recombination reaction, and specifically to determine if the carbon atoms exchange with other atoms in other acetylene molecules, tests using carbon isotopes were conducted. A mixture of 50% regular acetylene, C2H2, and 50% heavy acetylene. 

A flame-ionization, total hydrocarbon analyzer determines the THC, and the total carbon content is calculated as methane. Other methods include catalytic combustion to carbon dioxide, which may be deterrnined by a sensitive infrared detector of the nondispersive type. Hydrocarbons other than methane and acetylene are present only in minute quantities and generally are inert in most appHcations. 

Acetylene has a low solubiHty in Hquid oxygen. Excessive concentrations can lead to separation of soHd acetylene and produce accumulations that, once initiated, can decompose violently, detonating other oxidizable materials. Acetylene is monitored routinely when individual hydrocarbons are determined by gas chromatography, but one of the wet classical methods may be more convenient. These use the unique reaction of acetylene with Ilosvay s reagent (monovalent copper solution). The resulting brick-red copper acetyHde may be estimated colorimetricaHy or volumetricaHy with good sensitivity (30). 

Quantitative aluminum deterrninations in aluminum and aluminum base alloys is rarely done. The aluminum content is generally inferred as the balance after determining alloying additions and tramp elements. When aluminum is present as an alloying component in alternative alloy systems it is commonly deterrnined by some form of spectroscopy (qv) spark source emission, x-ray fluorescence, plasma emission (both inductively coupled and d-c plasmas), or atomic absorption using a nitrous oxide acetylene flame. 

Gas yield, the most impoitant specification for acetylene-giade carbide, is determined by slaking the carbide in water, collecting and measuring the volume... 

Stmctural variations of the reagents used in these reactions have been a primary source of progress in dye synthesis. Acetylenic reagents for cyanine dye synthesis include the weU-known acetylenic quartemary salts as general electrophilic reagents for the preparation of carbocyanine dyes. A number of tautomeric pairs of acetylenic dyes have been prepared and their tautomeric equiUbria determined (dyes (26a), (26b)) (29). 

M. A. IT insky and G. Knorre proposed l-nitroso-2-naphthol as a reagent for cobalt and Zh.I. lotsich - magnesium diiodine acetylene as a reagent for carbonyl group. F.M. Flavitsky developed a method for qualitative analysis based on solid substances as well as a portable laboratory for qualitative analysis. G.V. Khlopin proposed a method for determining oxygen dissolved in water. 

Acetylene-block assay Estimates denitrification by determining release of nitrous oxide (NjO) from acetylene-treated soil. 

Although the emphasis in this chapter has been on tbe synthesis and mechanism of formation of simple enamines, brief mention will be made of the addition of amines to activated acetylenes to indicate the interest and activity in this area of substituted enamines. Since such additions tend to be stereospecific, inclusion in this section seems apropos. The addition of amines to acetylenes has been much studied 130), but the assigning of the stereochemistry about the newly formed double bond could not be done unequivocally until the techniques of NMR spectroscopy were well developed. In the research efforts described below, NMR spectroscopy was used to determine isomer content and to follow the progress of some of the reactions. 

The high reactivity of monosubstituted acetylenes in many reactions (acetylenic condensation, Favorsky reaction, Mannich reaction, oxidative coupling, etc.) is determined by their acidity (7IMI1 83MI1). The literature data on the thermodynamic CH acidity of these compounds are rather scarce. 

One of the most important routes to isoxazole and isoxazoline rings involving the formation of the 1—5 and 2—3 bonds involves the condensation of hydroxylamine with a,/8-unsaturated carbonyl compounds. This method was previously widely used, but it is now of no preparative value, though it has been recently applied to determine the configuration of oximes. " The only new modification of this synthesis is the use of the acetals (27) of a,/8-acetylenic aldehydes for preparation of 5-substituted isoxazoles (28)... 

As far as flame composition is concerned, it may be noted that an acetylene-air mixture is suitable for the determination of some 30 metals, but a propane-air flame is to be preferred for metals which are easily converted into an atomic vapour state. For metals such as aluminium and titanium which form refractory oxides, the higher temperature of the acetylene-nitrous oxide flame is essential, and the sensitivity is found to be enhanced if the flame is fuel-rich. 

Amongst other devices used to produce the required atoms in the vapour state are the Delves cup which enables the determination of lead in blood samples the sample is placed in a small nickel cup which is inserted directly into an acetylene-air flame. The tantalum boat is a similar device to the Delves cup in this case the sample is placed into a small tantalum dish which is then inserted into an acetylene-air flame. The use of these devices, especially for small sample volumes, has now been largely superseded by the graphite furnace. 

The determination of magnesium in potable water is very straightforward very few interferences are encountered when using an acetylene-air flame. The determination of calcium is however more complicated many chemical interferences are encountered in the acetylene-air flame and the use of releasing agents such as strontium chloride, lanthanum chloride, or EDTA is necessary. Using the hotter acetylene-nitrous oxide flame the only significant interference arises from the ionisation of calcium, and under these conditions an ionisation buffer such as potassium chloride is added to the test solutions. 

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