N-Pentanal, by condensation

The conditions at which the separations are performed depend on the properties of the materials. Let us suppose we wish to separate n butane from n pentane. Table 4-3 gives the boiling points of these compounds. When possible the pressure in a distillation column is usually kept close to atmospheric. Since all multistage distillation columns require reflux, which is obtained by condensing the exiting vapor stream, if the top of the column were producing nearly pure butane the condensing temperature would be around 31°F( - 1°C). To obtain condensation at this temperature a coolant is needed at a temperature at least 10°F (5°C) cooler. This means that... 

A solution of 10.5 g. (0.046 mol) of freshly distilled bis(tri-fluoromethyl)-l,2-dithiete (Note 2) in 200 ml. of n-pentane is cooled to —10° in a 1-1. round-bottomed flask equipped with an efficient reflux condenser and protected from moist air by a dry nitrogen blanket. A solution of 3.0 ml. (0.023 mol) of nickel carbonyl dissolved in 100 ml. of w-pentane is added down the condenser in one portion to this solution. The mixture is swirled to mix. An intense blue-violet color develops in about 15 to 20 seconds and after 1 to 2 minutes, vigorous evolution of carbon monoxide occurs. This evolution subsides in 10 minutes and the deep violet solution is allowed to warm to 0° during 2 hours to ensure complete reaction. Most of the pentane is removed by distillation at atmospheric pressure, the remaining 50 to 60 ml. is removed in vacuo (0.1 mm.), and the resultant crystalline mass is evacuated (0.1 mm.) at 50° for 4 hours. The crude product consists of shiny black-purple needles and weighs 11.8 g. (98%). Recrystallization from dry benzene (Note 3) gives shiny black crystals, m.p. 134 to 135° (sealed tube). The complex is air-stable but should be kept out of contact with moist air. 

The preparation of the catalyst starts with the synthesis of 1-mes-ityl-3-(7-octene)-imidazole bromide. This compound is prepared by condensing mesityl imidazole with 8-bromooctene. The resulting salt is deprotonated with (TMS)2NK, where TMS is the tetrameth-ylsilyl radical. This step is performed in tetrahydrofuran at -30°C for 30 min. To this product a solution of the ruthenium complex (PCy3)2Cl2Ru=CHPh is added at 0°C. Bringing the solution slowly to room temperature, after 1 h the ligand displacement was determined to be complete. Afterwards, the reaction mixture is then diluted with n-pentane and heated to reflux for 2 h to induce intramolecular cyclization. 

The following procedural details were recommended by the checker. At least ten times as much re-pentane should be used as boron tribromide. A reflux condenser is needed to return the n-pentane, and a bubbler is needed to monitor the addition of trimethylamine. 

The apparatus for the preparation of n-butyllithium - consists of a three-necked flask fitted with a mercury-sealed stirrer, a dropping fuimel, and a reflux condenser. The apparatus is assembled hot, and air is immediately displaced by a stream of dry nitrogen which enters through the condenser. A solution of 37 ml. (0.35 mol) of n-butyl chloride in 50 ml. of n-pentane is added slowly (about one drop per second) to small pieces of lithium wire (5.0 g. 0.71 mol) suspended in 80 ml. of 71-pentane. Reaction begins after a short induction period (about 10 minutes), producing a... 

About 2 ml. of the methyl iodide solution is added to the stirred mixture, and after about 10 seconds, the stopcock is opened for a minute. This process is repeated until the dimethyl sulfoxide solution is colorless. The crude methylphosphine which collects in the liquid-nitrogen-cooled trap is then purified by fractional condensation in traps cooled to —112° (CS2 slush), — 130° (n-pentane slush), and —196° (liquid nitrogen). The material which collects in the —112 and —196° traps is discarded. About 0.009 mole (75% yield) of purified methylphosphine collects in the —130° trap. 

N 18.18% solid, mp 84—85° bp — expl at higher temp can be ptepd by nitration of product obtd by condensation of l,5 dinitro-pentane with formaldehyde... 

The combination of acidic and oxidizing properties of vanadyl pyrophosphate makes several different transformations possible over paraffins, as illustrated by the scheme in Figure I for the reactions which may occur on n-pentane. The relative contribution of the different pathways (i.e., cyclization of intermediate olefin or dienic compound vs. O-insertion, or dimerization vs. cyclization) is a function of the nature of the reactant and of the availability of surface oxidizing centres or of sites which can favour the dimerization or condensation reactions. 

The following dimers could be formed by condensation of two molecules of n-pentane ... 

Absorber and strippers may be classified as complex columns because they possess two feeds and because they possess neither an overhead condenser nor a reboiler. The sketch of the absorber in Fig. 4-1 depicts an historic application of absorbers in the natural gas industry. From a light gas stream such as natural gas that contains primarily methane plus small quantities of, say, ethane through n-pentane, the desired quantities of the components heavier than methane may be removed by contacting the natural gas stream with a heavy oil stream (say n-octane or heavier) in a countercurrent, multiple-stage column such as the one shown in Fig. 4-1. Since absorption is a heat-liberating process, the lean oil is customarily introduced at a temperature below the average temperature at which the column is expected to operate. The flow rate of the lean oil is denoted by L0, and the lean oil enters at the top of the column as implied by Fig. 4-1. The rich gas (which is sometimes called the wet gas) enters at the bottom of the... 

These results, while specific to this system, have some interesting implications for the purification of mixtures. For example, suppose that by starting with a liquid mixture of 50 mol % n-pentane and 50 mol % /i-heptane, we wanted to produce a liquid mixture that contained 98 mol % /j-pentahe. One way to do this would be to vaporize some of the initial mixture, collect the vapor, and then condense it. However, we see from the results above that the highest concentration of n-pentane we could get in this way is 88.8 mole %, but only if we got an infinitesimal amount of vapor (i.e., L = 1). Vaporizing any greater fraction of liquid produces a vapor of lower concentration, as seen above. 

We see from these results that by vaporizing 20 mol % (L = 078 for stage 2) of the condensed vapor from stage 1, we obtain. a vapor that contains the desired 98 mol % n-pentane. So we have met the concentration specifications. However, this process is very wasteful of the chemicals and not energy efficient. In particular, if we started with 100 moles of the initial feed, only 10 moles would remain after the first partial vaporization, and only 2 moles of the product stream containing 98 mol % n-pentane would result from the second stage. So that by starting with 50 moles of n-pentane (100 moles X 50 mol % n-pentane) we have obtained a product that contains only 2 moles X 98 mol % n-pentane = 1.96 moles of n-pentane. That is, 48.04 moles of n-pentane have not been recovered in the process. 

As indicated in the sketch below, a mixture of propane and n-pentane is to be separated by distillation at lOOpsia. Two designs are to be made by the Ponchon-Savarit method. In the first design, a total overhead condenser and a partial bottoms reboiler are to be used with saturated reflux at a flow rate of twice the minimum value. In the second design, a total overhead condenser, an inter-... 

The crude stibine, with its impurities of water and carbon dioxide, is distilled into an ampul attached to the ball joint which was previously connected to the reaction vessel. Trap 1 is immersed in a toluene slush bath ( — 95°) trap 2 is immersed in an n-pentane slush bath ( — 130°), and trap 3 is immersed in liquid nitrogen. By slowly distilling the crude stibine through these traps, the water with traces of stibine is condensed out in the — 95° trap, pure stibine is collected in the —130° trap, and the carbon dioxide with traces of stibine is collected in the liquid-nitrogen trap. With suitable precautions (because of the poisonous nature of stibine), the contents of traps 1 and 3 are discarded. Typically, 0.025 mol, or 560 cc. (S.T.P.), of purified stibine is prepared by this procedure. This corresponds to a 51% yield, based on the tetrahydroborate consumed. 

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