Extraction with bases

Several modifications of procedures based on halophosphonium ion have been developed. Triphenylphosphine and imidazole in combination with iodine or bromine gives good conversion of alcohols to iodides or bromides.22 An even more reactive system consists of chlorodiphenylphosphine, imidazole, and the halogen,23 and has the further advantage that the resulting phosphorus by-product diphenylphosphinic acid, can be extracted with base during product workup. 

Oxidation by the Dess-Martin Reagent. Another reagent that has become important for laboratory synthesis is known as the Dess-Martin reagent,28 which is a hypervalent iodine(V) compound.29 The reagent is used in inert solvents such as chloroform or acetonitrile and gives rapid oxidation of primary and secondary alcohols. The by-product, o-iodosobenzoic acid, can be extracted with base and recycled. 

In the first step (ij) the ylides 3 (R1 = H) can be alkylated with primary alkylhalogenide or with ethyl bromoacetate they can also be acylated with acetic anhydride in a reverse addition operation, (In spite of trans-ylidation process, the acylated phosphonium salt can be easily purified by liquid -liquid extraction with bases). Semi-stabilized ylides3(R1= 0) are not reactive enough to be alkylated or acylated in this way. 

Extraction with bases and tetralin/water mixtures... 

The naphthoquinones with acid hydroxyl function like lapachol are easily extracted with bases. They are also extracted in a Soxhlet apparatus with EtOH, and the resulting extract is then exhaustively extracted with AcOEt to yield a residue rich in naphthoquinones [115-116]. The naphthoquinones are mainly isolated from the wood and heartwood but there some examples of isolation from the roots [46, 48, 53, 58, 65, 66, 75, 78]. The study of commercial herbal products sold as Taheebo, Pau d Arco, Lapacho, and Ipe roxo carried out by Girard et al [117], showed important differences in the content of lapachol and other related naphthoquinones present in extracts of Tabebuia ssp Tabebuia rosea, T. cassinoides, T. impetiginosa, and T. chrisantha. Similar works using HPLC techniques have been carried out by Awang et al. [118]. 

Alkaloids are a group of nitrogen-containing natural products that occur primarily in higher plants, although they are also found in some fungi, such as mushrooms. The name alkaloid (meaning alkali-like ) is applied because they are amines and thus basic. Their basic character allows them to be readily isolated from their plant source. The plant material is extracted with aqueous acid. This converts the alkaloid to an ammonium cation, which is water soluble. Neutralization of the acidic extract with base causes the alkaloid to precipitate. 

Most amino acids are readily available to chemists. If proteins are hydrolysed with, say, concentrated HC1, they are broken down into their amino acids. This mixture is tricky to separate, but the acidic ones are easy to extract with base while the aromatic ones crystallize out easily. 

In addition to the water-soluble and insoluble members of the condensed tannin family, both of which are soluble in polar organic solvents, there is a third related fraction, usually called a phenolic acid. This material can only be isolated by extraction with aqueous alkaline solutions or with sodium sulfite or bisulfite solution at elevated temperatures and pressures. Since the tannins and phlobaphenes are also soluble in aqueous base, they will be coextracted from bark along with the phenolic acids when bark is extracted with base. This is important to remember in the subsequent discussion on bark-based adhesives. 

Vacuum-still bottoms from the H-coal liquefaction process were separated into acid, neutral, and basic fractions by precipitation with acids or by extraction with bases. About one-third of the preasphaltene and one-sixth of the asphaltene fraction were precipitated by acids equivalent weights of the bases were in the range 1200-1800 for preasphaltenes and 600-800 for asphaltenes. The acidic components were obtained either by extraction with aqueous sodium hydroxide or by extraction with benzyltrimethylammonium hydroxide in methanol. About one-fifth of the asphaltene and one-fourth of the presasphaltene fractions were obtained as acids, and up to 10% as amphoteric substances. Nitrogen and sulfur were present in all fractions found. Deno axidation (CF3C02H, H202, H 04) gave dicarboxylic acids from malonic to adipic in addition to mono acids. 

The dichloromethane filtered from the binder and acetaminophen mixture (Solution 1) should contain caffeine and aspirin. These can be separated by extraction either with acid, which will remove the caffeine as a water-soluble salt, or by extraction with base, which will remove the aspirin as a water-soluble salt. We shall use the latter procedure. 

Research on the chemical properties of humic substances was extended by the Swedish investigator Berzelius (1839). One of his main contributions was the isolation of two light-yellow-colored humic substances from mineral waters and a slimy mud rich in iron oxides. They were obtained from the mud by extraction with base (KOH), which was then treated with acetic acid containing copper acetate. A brown precipitate was obtained ctilled copper apocrenate. When the extract was neutralized, another precipitate was obtained, called copper crenate. The free acids, apocrenic and crenic acids, were then brought into solution by decomposition of the copper complexes with alkali. These newly described humic substances were examined in considerable detail, including isolation, elementary composition, and properties of their metal complexes (Al, Fe, Cu, Pb, Mn, etc). 

All comparisons of the elemental composition of soil humates with aquatic humates must be viewed with caution. In recent years, the extraction methodology has changed rapidly. A soil sample extracted with base in the classical manner may have up to 20% carbohydrate and up to 10% ash, while a sample extracted with XAD resins may have less than 2% carbohydrate and 2% ash. To compare two samples extracted by two different methods would be akin to comparing apples and oranges. Fortunately, a body of literature is accumulating which reports the properties of humates extracted by a single, well-defined method. 

The inhibitor can be removed by extraction with base using a procedure similar to that for EGDMA, see footnote a, Protocol 1b, above. 

Racemic A,A -dimethyl-l,2-diphenylethylenediamine was treated with L-(+)-tartaric acid to afford a pair of diastereomeric salts which were separated overnight by selective precipitation from ethanol. The (R,R)-diamine was separated by filtration, followed by extraction with base to remove the tartartic acid. Removal of the solvent produced the crude diamine in 90% yield and greater than 99% ee. The (5,5)-diamine was isolated by concentration of the mother liquor and the same extraction procedure to... 

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