Stearic acid melting point

The purity and melting point of the final product are dependent on the purity of the stearic acid. If Armour s Neo-Fat 1-65, m.p. 64-67° (90-95% stearic acid) is recrystallized first from 95% ethanol and then from acetone, a stearic acid melting from 67° to 68° results which yields a stearone with a melting point of 88-89° (shrinks at 86-88°). 

The interaction between zinc oxide and stearic acid in a medium suitable to simulate a vulcanized system has been investigated [65] experimentally using vibrational spectroscopic technique. Confocal Raman micro spectroscopy revealed that at ambient temperature both components are phase-separated in the form of microcrystals. When the reaction temperature (SO C and above) is reached only zinc oxide is present in the form of particles while the stearic acid melts and gets molecularly dispersed within the rahher matrix. The analysis points to a core-shell structure of the reacting system stearic acid diffuses to the surface of zinc oxide domains causing the shrinkage of the zinc oxide core and the formation of a shell of increasing thickness made of zinc stearate. 

Branched-chain acids contain at least one branching alkyl group attached to the carbon chain, which causes the acid to have different physical, and in some cases different chemical, properties than their corresponding straight-chain isomers. For example, stearic acid has a melting point of about 69°C, whereas isostearic acid has a melting point of about 5°C. Some properties of commercial branched-chain acids are shown in Table 1 (1,2). 

Specialty waxes include polar waxes for more polar adhesive systems. Examples would be castor wax (triglyceride of 12-hydroxy stearic acid) or Paracin wax N- 2 hydroxy ethyl)-12-hydroxy stearamide) which are used in polyester, polyamide, or with high VA EVA copolymer-based systems. Other common polar waxes are maleated polyethylenes, which are used to improve the specific adhesion of polyethylene-based adhesives, and low molecular weight ethylene copolymers with vinyl acetate or acrylic acid, which are used to improve low temperature adhesion. High melting point isotactic polypropylene wax (7 155°C) and highly refined paraffin wax (7,n 83°C) are used where maximum heat resistance is critical. Needless to say, these specialty waxes also command a premium price, ranging from 2 to 5 times that of conventional paraffin wax. 

Modification of filler s surface by active media leads to the same strong variation in viscosity. We can point out as an example the results of work [8], in which the values of the viscosity of dispersions of CaC03 in polystyrene melt were compared. For q> = 0.3 and the diameter of particles equal to 0.07 nm a treatment of the filler s surface by stearic acid caused a decrease in viscosity in the region of low shear rates as compared to the viscosity of nontreated particles more than by ten times. This very strong result, however, should not possibly be understood only from the point of view of viscometric measurements. The point is that, as stated above, a treatment of the filler particles affects its ability to netformation. Therefore for one and the same conditions of measuring viscosity, the dispersions being compared are not in equivalent positions with respect to yield stress. Thus, their viscosities become different. 

On the other hand, in order to preserve the cold properties of the fuel (Cloud Point, Pour Point and low-temperature filterability), it is mandatory not to increase the melting point, that in turn depends on both the saturated compound (stearic acid, C18 0) content and the extent of cis/trans and positional isomerization as the difference in melting point between the cis and trans isomer is at least 15°C according to double bond position as shown in Table 1. 

In order to obtain stearone with the highest melting point, the checkers found it necessary to purify the above recrystallized stearic acid by converting it to the methyl ester and fractionat-... 

Fatty acids have also been converted to difunctional monomers for polyanhydride synthesis by dimerizing the unsaturated erucic or oleic acid to form branched monomers. These monomers are collectively referred to as fatty acid dimers and the polymers are referred to as poly(fatty acid dimer) (PFAD). PFAD (erucic acid dimer) was synthesized by Domb and Maniar (1993) via melt polycondensation and was a liquid at room temperature. Desiring to increase the hydrophobicity of aliphatic polyanhydrides such as PSA without adding aromaticity to the monomers (and thereby increasing the melting point), Teomim and Domb (1999) and Krasko et al. (2002) have synthesized fatty acid terminated PSA. Octanoic, lauric, myristic, stearic, ricinoleic, oleic, linoleic, and lithocholic acid acetate anhydrides were added to the melt polycondensation reactions to obtain the desired terminations. As desired, a dramatic reduction in the erosion rate was obtained (Krasko et al., 2002 Teomim and Domb, 1999). 

Esterification of at least 45% of the hydroxyl groups with long chain fatty acids, e.g., stearic or behenic acid, results in a semi crystalline material (side chain crystallization). The obtained materials are characterized by melting point ranges which are approximately 10 °C lower than the comparable methyl esters. 

The F, T curve beyond this point is again linear, but the surface pressure decreases rapidly with elevation of the temperature until the point B is reached where an abrupt change in the slope of the curve is noted, in many cases such as in the long chain esters the film is found to be condensed at A and expanded at B, thus AB is the expansion interval of Labrouste and Adam. For acids on the other hand with the exception of stearic, the film is already expanded at the melting point and the portion of the curve AB is missing. 

Melting Points of Lipids The melting points of a series of 18-carbon fatty acids are stearic acid, 69.6 °C oleic acid, 13.4 °C linoleic acid, - 5 °C and linolenic acid, - 11 °C. (a) What structural aspect of these 18-carbon fatty acids... 

The reaction mechanism for the selective hydrogenation of edible oils is very complex. Figure 14.1 illustrates a reaction scheme for linoleic acid. In this scheme, (n m) is used to represent an oil with n carbon atoms and m double bonds. There are several parallel, consecutive, and side reactions. Oleic acid (cis 18 1) is the desired product when the reaction starts with linolenic (all-cis 18 3) or linoleic acid (cis, cis 18 2). In the hydrogenation of linolenic and linoleic acid, elaidic acid (trans 18 1) is formed in a cisjtrans isomerization reaction. From the viewpoint of dietics, elaidic acid is an undesirable product however, its presence increases the melting point of the product in a desirable way. Stearic acid (18 0) is formed in a consecutive reaction, but direct formation from linoleic acid is also possible. 

Because the lipid components of membranes must be in a fluid state to function as membranes in living cells, it is reasonable to assume that primitive membranes in the first forms of cellular life must also have had this property. Straight-chain hydrocarbons have relatively high melting points due to the ease with which van der Waals interactions can occur along the chains. Any discontinuity in the chains interrupts these interactions and markedly decreases the melting point. As an example, stearic acid contains 18 carbons in its alkane chain and melts at 68 °C, while oleic acid, with a cis-double bond between carbons 9 and 10, has a melting point near 14 °C. If cellular life today requires fluid membranes, it is reasonable to assume that the earliest cell membranes were also composed of amphiphilic molecules in a fluid state. 

Melting Points of Lipids The melting points of a series of 18-carbon fatty acids are stearic acid,... 

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