Water-removable bases

Water-removable bases are basically oil-in-water emulsions. Unlike hydrocarbon and absorption bases, a large proportion of aqueous phase can be incorporated into water-removable bases with the aid of suitable emulsifying agents. It is easy to remove these bases from the skin due to their hydrophilic nature. Hydrophilic ointment USP is an example of a water-removable ointment base. 

Water-Removable Bases (Water-Washable Creams)... 

Step 2. Extraction of the basic components. Extract the ethereal solution (Ej) with 15 ml. portions of 5 per cent, hydrochloric acid until all the basic components have been removed two or three portions of acid are usually sufficient. Preserve the residual ethereal solution (E2) for the separation of the neutral components. Wa.sh the combined acid extracts with 15-20 ml. of ether discard the ether extract as in Step 1. Make the acid extract alkaline with 10-20 per cent, sodium hydroxide solution if any basic component separates, extract it with ether, evaporate the ether, and characterise the residue. If a water-soluble base is also present, it may be recognised by its characteristic ammoniacal odour it may be isolated from the solution remaining after the separation of the insoluble base by ether extraction by distilling the aqueous solution as long as the distillate is alkahne to htmus. Identify the base with the aid of phenyl iso-thiocyanate (compare Section 111,123) or by other means. 

Protonolysis. Simple trialkylboranes are resistant to protonolysis by alcohols, water, aqueous bases, and mineral acids. In contrast, carboxyUc acids react readily with trialkylboranes, removing the first alkyl group at room temperature and the third one at elevated temperatures. Acetic and propionic acids are most often used. The reaction proceeds with retention of configuration of the alkyl group via a cycHc, six-membered transition state (206). 

To effectively remove carbonyl sulfide from a gas stream, special alkaline scmbbiag Hquors are used. These contain sodium aluminate or sodium plumbite, or they are made of alkaUes with a hydrolysis catalyst based on Zn, Fe, Ni, or Cu. Diethanolamine, diglycolamine, or other alkanolamines (qv) mixed with water remove carbonyl sulfide from sour, ie, acid-gas-containing, gas streams (25,26) (see Carbon dioxide). 

The simplest and cheapest procedure to obtain standards is based on selective extraction followed by crystallization. A method developed to obtain lycopene from tomato residue using factorial experimental design consisted of a preliminary water removal with ethanol, followed by extraction with EtOAc and two successive crys-talhzation processes using dichloromethane and ethanol (1 4), producing lycopene crystals with 98% purity, measured by HPLC-PDA. Using this approach, bixin was extracted with EtOAc from annatto seeds that were previously washed with... 

Pervaporation Membranes Pervaporation has a long history, and many materials have found use in pervaporation experiments. Cellulosic-based materials have given way to polyvinyl alcohol and blends of polyvinyl alcohol and acrylics in commercial water-removing membranes. These membranes are typically solution cast (from... 

Puig, S., et al., An on-line optimisation of a SBR cycle for carbon and nitrogen removal based on on-line pH and OUR The role of dissolved oxygen control, Water Sci. Tech., 53,171, 2006. 

The slow water removal is obvious within the synthesis of, for example, myristyl myristate determining the total reaction time. In a stirred-tank reactor it takes 24 h to reach a conversion of 99.6% and in a fixed-bed reactor 14 h. Therefore, a new synthesis platform (Figure 4.11) which also enables conversion of highly viscous polyols and fatty acids from renewable resources to ester-based surfactants was designed. It is used by Evonik on a pilot scale, outperforming conventional methods, such as stirred-tank or fixed-bed reactors. In contrast to the setups introduced before, conversion of >99.6% is already obtained after 5.5 h in the bubble column reactor [44-47]. 

Other water-soluble polymers which do not tend to suffer from problems of retrogradation are sometimes used when different properties are required. Soluble cellulose derivatives, particularly car-boxymethyl cellulose, which is prepared by reaction of high purity cellulose with chloroacetic acid in the presence of alkali (equation 8.1), is popular for surface sizing base papers which are subsequently to be coated, because it assists in water removal when the coating mix is applied. 

Ointments are semisolid preparations that are intended for external use. Ointments may contain either finely powdered drugs or their mixtures, liquids, and other drug forms incorporated into appropriate bases. They are applied to the skin for their physical effects as emollients (which make the skin more pliable), protectants, lubricants, and drying agents. Ointment bases are also used as vehicles in which to incorporate topical medications which exert specific effect. There are four types of ointment bases, namely, oleaginous, absorption, water removable, and water soluble bases. 

The research group led by Zhou [68,69] has also investigated the use of perforated materials as cathode DLs in PEMFCs through modeling. However, the group s model results were produced based only on conservation of mass and momentum (i.e., energy and electrochemical equations were not considered). This model studied only how different shapes of perforations affected the liquid water removal through the DL. 

The range of pA a values that can be measured in water is determined by the ionization of water itself, i.e. —1.74 (the pA a of H3O+) to 15.74 (the pATa of H2O) see Box 4.1. Acids that are stronger than H3O+ simply protonate water, whereas bases that are stronger than HO remove protons from water. 

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