Cleaning mixtures

The most widely used cleansing agent is the chromic acid cleaning mixture. It is essentially a mixture of chromic acid (CrOj) and concentrated sulphuric acid, and possesses powerful oxidising and solvent properties. Two methods of preparation are available —... 

It must be emphasised that there is no universal cleaning mixture. The student must take into account the nature of the substance to be removed and act accordingly. Thus if the residue in the flask is known to be basic in character, dilute hydrochloric or sulphuric acid may dissolve it completely similarly, dilute sodium hydroxide... 

A method which is frequently used consists in filling the apparatus with chromic acid cleaning mixture (CARE), a nearly saturated solution of powdered sodium dichromate or potassium dichromate in concentrated sulphuric acid, and allowing it to stand for several hours, preferably overnight the acid is then poured off, the apparatus thoroughly rinsed with distilled water, and allowed to drain until dry. [It may be mentioned that potassium dichromate is not very soluble in concentrated sulphuric acid (about 5 g per litre), whereas... 

After use the cells must be carefully washed with distilled water, or if an organic solvent which is not miscible with water was employed, they must be rinsed with a solvent which is miscible with both the solvent used and with water, and then well washed with distilled water. Finally, they are rinsed with ethanol followed by drying, which may be conveniently done in a vacuum desiccator. Cells which have become contaminated can usually be cleaned by soaking in a solution of a detergent, such as Teepol. For obstinate contamination recourse may be made to the use of sulphuric acid-sodium dichromate cleaning mixture (CAUTION ) (Section 3.8). After soaking overnight the cells are well washed with water and finally dried. 

For the galactosylation reactions, 2,3,4,6-tetra-O-benzylgalactopyranosyl trichloroacetimidate 2 and dibenzylphosphite 10 were used as donors (Table 12.1). Under these conditions, the (5-(l—>3)- and (5-(l—>4)-linked disaccharides 16 and 17 were formed in only minor amounts (entries 1 and 2). To increase the proportion of the (5-anomers, the peracetylated galactopyranosyl trichloroacetimidate 11 was used as the donor. Reactions were poor in DMF, but in dioxane, a clean mixture of products was obtained. Two equivalents of donor were required to give a conversion of 20-30% of 1 to disaccharides 13-18. Peaks eluting when the column was washed with more polar solvent mixtures suggested that only traces of trisaccharides were formed, but the identity of these peaks was not investigated. 

Fig. 5. Etching rate of some back-end materials in different nonoxidant cleaning mixtures adjusted to etch 5 nm of PECVD TEOS oxide in 10 min.

Chromic acid cleaning mixture, 53 Chromophores, 1144-1146 three conjugated, 1146 two conjugated, 1146 typical single, 1145 Chrysoidine, 620, 623 Cinnamic acid, 707, 712, 1113... 

Cleaning of Laboratory Glassware and Cleaning Mixtures. See Lange (1961), 1776... 

It must be emphasised that there is no universal cleaning mixture. The chemist must take into account the nature of the substance to be removed and the amount of deposit, and act accordingly. Thus if the residue in the flask is known to be basic in character, dilute hydrochloric or sulphuric acid may dissolve it completely similarly, dilute sodium hydroxide solution may be employed for acidic residues. In these instances the acidic or basic aqueous solution may be washed down the drain with liberal quantities of water. If the residue is known to dissolve in an inexpensive organic solvent, this should be employed in such a case the solution must be poured into the appropriate residues bottle, not down the sink. Solvent suitable specifically for cleaning use may be recovered by distilling accumulated residues. Remaining heavily contaminated material should be suitably disposed of (Section 2.1, p. 30). 

Sulphuric acid (concentrated and oleum ) - should always be mixed with water very carefully, by pouring into cold water as a thin stream to prevent acid splashes or spray. Chromic acid cleaning mixtures have the corrosive properties of concentrated sulphuric acid as well as the dangerous oxidising properties of the chromic acid. 

Bore cleaning products include an electrochemical cleaning device and numerous chemical cleaning mixtures, containing both organic and inorganic compounds, the compositions of which are commercial secrets. 

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