Acid migration

Why does the amount of acid in paper make such a difference Acids are corrosive chemicals. Corrosive chemicals can destroy material or living tissue on contact. Paper does not contain enough acid to burn skin, but over time the paper becomes stiff and brittle and eventually falls apart. As a result, precious personal memories or important historical documents that were written on acidic paper can be lost. Acid-containing paper can also transfer the acid to other objects in a process called acid migration. The acid can weaken or destroy the fibers in fabrics. It can also ruin photographs. Therefore, to preserve those irreplaceable memories, be sure to use paper that is acid-free. 

As discussed in Chapter 11, electrophoresis refers to a group of techniques used to separate and study molecules with electrical charges. Based upon these charges, both sign and magnitude, biomolecules such as proteins, peptides, amino acids, nucleic acids, and fragmented nucleic acids migrate in an electrical... 

At pH 2, all amino acids migrate electrophoretically towards the cathode... 

To which pole will an amino acid migrate at a pH above its isoelectric point ... 

Problem 21.7 (a) How does one repress the ionization of an a-amino acid (b) The pH at which [anion] = [cation] is called the isoelectric point. In an electrolysis experiment, do a-amino acids migrate at the isoelectric p>oint ... 

These same types of compounds are also more resistant to many acids at high temperatures than natural rubber can handle. Neoprene should not be used in parts which are bonded to metal for hydrochloric acid service because acid migration can cause failures. For hydrochloric acid service ebonite lined mild steel equipment is the correct selection. Ebonites form rubber hydrochloride film in contact with natural rubber and this film is the protective layer against corrosion. 

When the catalyst is a Bronsted acid, migration is not stereospecific. Under these conditions, syn and anti forms are readily interconverted, presumably via the pathway shown in Equation 6.55. 

The lysoPS migrates to an Rf of 0.2, and the free fatty acid migrates to an /Rvalue of 0.70. These compounds can be isolated from the plates and studied further as desired. 

Books often have notes, tickets, and much other extraneous matter inserted between the leaves or inside the front cover. This throws undue strain on the joints, so, ideally, all such matter should be removed and kept in an acid-free envelope along-side the book. Apart from causing mechanical damage, such material is often acid, and this may result in acid migration and the staining and embrittlement of adjacent leaves. 

More active aromatic compounds, such as resorcinol and a-naphthol, are carboxylated in excellent yields by heating their alkali salts with carbon dioxide (Kolbe reaction). The carboxyl group of salicylic acid migrates to the para position when this compound is heated to 240° with potassium carbonate the p-hydroxybenzoic acid is obtained in 80% yield. ... 

Mild conditions should be employed in alkaline hydrolysis of olefinic esters. Double bonds in many acids migrate readily during saponification. Aqueous alcoholic sodium hydroxide is used in the preparations of 3-ethyl-3-pentenoic acid (56%) and /S-methylcinnamic acid (41%). ... 

Mobile phases of hexane or light petroleum ether as main components and acetone or diethyl ether as polar modifiers are used for the separation of simple lipids. Acetic or formic acid is often added to keep the free fatty acids in the fully protonated form. The retention of simple lipids increases in the order waxes, sterol esters, methyl esters, triacylglycerols, free fatty acid, sterols, dia-cylglyerols, and monoacylglycerols (see Fig. la). If no acid is present in the mobile phase, the free fatty acids migrate between diacylglyerols and monoacylglycerols. The... 

Different amino acids migrate at different rates, depending on their isoelectric point and on the pH of the aqueous buffer. Thus, the different amino acids can be separated. Figure 26.1 illustrates this separation for a mixture of lysine (basic), glycine (neutral), and aspartic acid (acidic). 

Catalytic reduction of thebaine in 2-2-5N hydrochloric acid results in hydrolysis of the dihydrothebaine [xi] first formed, the product being a mixture of dihydrothebainone [xn] and dihydrocodeinone [xv] [19-21] in 5N hydrochloric acid migration of the side-chain occurs and metathebainone [xvi] is formed [19] (see below). 

Fig. 7 a Relative amount of monomeric hydroxy acids migrating from the crosslinked CL/DXO copolymers, (b) Mass loss of the crosslinked CL/DXO copolymers. ( ) CLIOO, ( ) CL80, (A) CL60, (x) CL40, (o) CL20 and ( ) CLO dming the hydrolysis. The name of the material indicates the caprolactone content in the polymer, e.g. CL80 has 80 mol % caprolactone nnits and 20 mol % DXO-nnits. Reprinted from [159] with permission of American Chemical Society. American Chemical Society (2007)... 

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