Foaming During Distillation

The following abbreviadons are used in this book for some solvents and reagents  

Purities of the end products in the procedures are generally 95%. The boiling points given refer to small intermediate fractions. 

Detailed information about the use, handling and disposal of strongly basic reagents and allcali metals is given in Chapter I of Preparative Polar Organometaliic Chemistry, Vol. 1 [1], 

Various organolithium compounds are available today in technical amounts information about handling the material is supplied by ChemetaU GmbH, Reuterweg 14, D-6000 Frankfurt am Main 1, F.R.G. 

---

Careful washing with brine is important to avoid foaming during distillation. 

The higher the surface tension the more likely it is to make foam during distillation and this can result in filling the column with a stable froth which will prevent fractionation. A tray column, that creates mass transfer by bubbling vapour through liquid, is much more vulnerable to foam formation than a packed column which does not rely upon bubbling. 

Note 6—Silicone higb-vacuum grease has been used for this purpose. An excess of this lubricant applied to the flask joint can cause the sample to foam during distillation. 

The sample is normally placed in a round-bottom flask and dispersed in water. The aqueous slurry can be heated directly (with continuous stirring) to carry over the steam-distillable components. Problems can be encountered due to scorching of the sample if too much heat is applied, and in addition bumping may occur when the sample contains particulates. Stirring may prevent these problems. Foaming is another potential problem. Many food products contain surface-active agents and will foam during distillation addition of antifoams (e.g., DC polydimethyl siloxanes) may prevent this problem, but these silicones usually end up in the distillate, as evidenced by GC-MS peaks at m/z = 73, 147, 207, 221, 281, and 341. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

The inlet tube for steam should reach to the bottom of the distillation flask. A i6-mm. bulb on the end of this tube with four 0.8-mm. openings helps to insure thorough mixmg of the heavy residue. If this is not well stirred the aldehyde distils very slowly. It is well to connect the flask to the condenser through a large Hopkins still head in order to prevent the entrainment of foam during the distillation. 

There is some tendency toward foaming during the steam distillation. To avoid this the flask should be submerged almost completely in the oil bath. 

An excess of sodium carbonate promotes foaming during the distillation, and is to be avoided. Since the neutral point is not easily recognized with test paper, the carbonate is added in decreasing amounts, until, a fresh portion is no longer decomposed with gas evolution. 

Vigorous magnetic stirring of the pot material prevents excessive foaming during the distillation. 

To avoid foaming during the distillation, the checkers removed the last traces of solvent by evacuation at 0.1 mm. and room temperature for 12-24 hours. 

The submitters had originally distilled the volatile products from this mixture, containing mainly polymeric material, by a more conventional procedure. However, the checkers found the problems from foaming during the distillation so severe that the alternative low-temperature distillation procedure was adopted. 

The free amine rapidly absorbs carbon dioxide. It is therefore essential to protect the distillation apparatus from the atmosphere with a guard-tube filled with soda-lime. As the product tends to foam excessively during distillation, the apparatus used should be larger than is customary for the volume of liquid to be distilled. 

Flammable Liquid, Poison SAFETY PROFILE Poison by ingestion. Moderately toxic by skin contact. A skin and eye irritant. A dangerous fire hazard when exposed to heat, flame, or oxidizing materials. To fight fire, use alcohol foam. Reacts with air to form explosive peroxides. Violent explosions have occurred during distillation. When heated to decomposition it emits acrid smoke and fumes. See also ALLYL COMPOUNDS and ETHERS. 

Elimination of turbidity, haze, emulsions Improved filterability of process liquor and finished product Reduced tendency to foam during evaporation and distillation Faster rate of settling during clarification... 

In the distillation of solid foods, it is necessary to add water to the material in the flask. It is optional whether the water is tap, distilled, recently boiled distilled, or carbonated distilled water. The error due to the oxygen present in the water is negligible when compared to other possible errors. To avoid foaming during the initial period of distillation, it is desirable to add a small quantity of tannin or a few drops of mineral oil. Parafiffii will distill over and gum up the condenser and therefore should not be used. 

NOTE. The mixture tends to foam during the distillation, so care must be taken to prevent contamination of the distillate by cinnamon particles, especially if powdered cinnamon is used. If stick cinnamon is used, first evacuating the flask containing the water and cinnamon for a few minutes and then returning the system to atmospheric pressure will allow water to fill the pores of the bark and greatly aids in reducing the foaming problem (See Taber, D. F. Weiss, A. J.J. Chem. Educ. 1998, 75, 633). 

---