Siphon formation

Monocyclic Phosphoranes. - Further studies on the mechanism and stereochemistry of the Wittig reaction have been conducted by a combination of 1H, 13C and 3 P n.m.r.2k 25. The results show that at -18°C both ois and trans diastereomeric oxaphosphetans (e.g. 17 and 18) may be observed and their decomposition to alkenes monitored by n.m.r. Evidence was presented to suggest that during this process oxaphosphetan equilibration involving the siphoning of (17) into (18) occurred in competition with alkene formation. 

The reaction can, however, be made preparative for (91) by a continuous distillation/siphoning process in a Soxhlet apparatus equilibrium is effected in hot propanone over solid Ba(OH)2 (as base catalyst), the equilibrium mixture [containing 2% (91)] is then siphoned off. This mixture is then distilled back on to the Ba(OH)2, but only propanone (b.p. 56°) will distil out, the 2% of 2-methyl-2-hydroxypentan-4-one ( diacetone alcohol , 91, b.p. 164°) being left behind. A second siphoning will add a further 2% equilibrium s worth of (91) to the first 2%, and more or less total conversion of (90) — (91) can thus ultimately be effected. These poor aldol reactions can, however, be accomplished very much more readily under acid catalysis. The acid promotes the formation of an ambient concentration of the enol form (93) of, for example, propanone (90), and this undergoes attack by the protonated form of a second molecule of carbonyl compound, a carbocation (94) ... 

A further effect due to the absence of viscosity is the well-known formation of superfluid films with siphon effects [42 49]. 

And of the last two oarsmen in the bow, let the one be the siphonator, and the other to cast the anchor into the sea.. .. In any case, let him have in the bow the siphon covered with copper, as usual, by means of which he shall shoot the prepared fire upon the enemy. And above such siphon (let there be) a false bottom of planks also surrounded by boards, in which the warriors shall stand to meet the oncoming foes.. .. On occasion [let there be] formations immediately to the front [without maneuvers] so, whenever there is need, to fall upon the enemy at the bow and set fire to the ships by means of the fire of the siphons.. . . Many very suitable contrivances were invented by the ancients and moderns, with regard to both the enemy s ships and the warriors on them—such as at that time the prepared fire which is ejected (thrown) by means of siphons with a roar and a lurid (burning) smoke and filling them [the ships] with smoke.. . . They shall use also the other method of small siphons thrown (i.e., directed) by hand from behind iron shields and held [by the soldiers], which are called hand siphons and have been recently manufactured by oar state. For these can also throw (shoot) the prepared fire into the faces of the enemy.8... 

In recent tests on a 5-cm contactor, the CINC V-2 model, estimates of the upper weir diameter indicated an apparent weir diameter much larger than the actual one (Leonard et al., 2002). As this contactor has a covered upper weir, a siphon probably formed to cause the unexpected results. Note that a siphon could also be formed over the LW as it is always closed. To the author s knowledge, this phenomenon has never been observed. For normal contactor operation, even with a closed upper weir, a siphon will probably not form, as it occurs only at very high flow rates. When a siphon is formed, the general contactor operation represented by Equation 10.5 no longer applies, since it is assumed that the pressure over the liquid surface on both weirs is the same. The formation of a siphon is an area where more research is needed. Some work has been started in this area. Experimental and modeling work by Wardle (2008) showed that a siphon can form above the upper weir on a 5-cm contactor when it is covered. Holes drilled in this cover reduced the effect of the siphon. 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

Atherosclerosis mainly affects large- and mediumsized arteries. Extracranial manifestations at the carotid bifurcation statistically dominate the intracranial arteries. Besides typical manifestations at the carotid siphon or the vertebrobasilar junction, atherosclerosis is occasionally also found in peripheral intracranial vessel segments. Typical sequelae of atherosclerosis are stenosing plaque formations, ulcerations, dilatations or the evolution of fusiform aneurysms, which can be accompanied by extensive formation of thrombus. 

After the water was collected in the reaction vessel, 288 ppm ferrous sulfate was added. Addition of a stoichiometric quantity (100 ppm) of potassium permanganate thus resulted in formation of hydrous ferric and manganese oxides. Scavenging eflBciencies for this precipitation reaction have been reported previously (5, 6). The resulting suspension was agitated for 10-20 min and allowed to settle for 12-24 hr, after which the supernatant hquid was siphoned. The precipitate was removed and... 

To the extent that studies have been done, most of the results can be interpreted on the basis that siloxycarbene formation is a rapid reversible process in which the short-lived siloxycarbene must be trapped quickly by a kinetically acidic reagent. Competitive with this is a slower Norrish type I cleavage reaction, which only predominates when there is no good trapping agent present to siphon off the simultaneously formed siloxycarbene (equation 67). 

In gel chromatographs of the first generation, the volume of each fraction collected is measured separately. In the instruments of the second generation, the retention volume is measured continuously, most frequently by means of a siphon. This device can easily be automated and utilized for controlling the injection system, and, eventually also the pumping system and fraction collector. The drawback of the siphon is its sensitivity to the variations of interfacial tension of the effluent and to the formation of the film of grease on its walls. Both effects are pronounced especially in the aqueous mobile phases. Smaller retention volumes can be measured by means of the drop counters or capillary volumeters. From the point of view of aqueous eluents, the drop counters exhibit the same limitations as siphons. The capillary volumeters are based upon counting how many times the effluent fills up the fixed volume of a capillary. The results of both, drop counters and capillary volumeters, depend on the flow rate and on the physical characteristics of the effluent. 

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