Purification

4 Key excerpts on "Purification"

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  eBook - PDF

  Advanced Practical Organic Chemistry

  • John Leonard, Barry Lygo, Garry Procter(Authors)
  • 2013(Publication Date)
  • CRC Press

    (Publisher)

  209 chapter eleven Purification 11.1 Introduction When a crude product has been isolated from a reaction work-up, the next step is to purify it. The degree of purity required will depend to some extent on the use for which the sample is intended. A synthetic intermedi-ate might only require rough Purification, whereas a product for elemen-tal analysis would require rigorous Purification. This chapter describes the most important Purification, crystallization, distillation, sublimation, and chromatography techniques. It is assumed that the reader is famil-iar with the basic principles of these methods, so the emphasis here is on more demanding applications such as the Purification of air-sensitive materials and Purifications on a microscale. 11.2 Crystallization 11.2.1 Simple crystallization All crystallizations are based on the same principle: a solid compound is fully dissolved in a solvent (or solvents) at a particular temperature, the conditions of the solution are changed such that the solution becomes supersaturated in the compound to be crystallized, and the compound then crystallizes from the solution. Many compounds can crystallize in more than one polymorphic form. For example, snow and hail are differ-ent polymorphs of ice. The polymorph you get depends on the conditions under which the crystallization takes place. Polymorphs have different melting points and stabilities, so if you have difficulty in obtaining good crystals from one crystallization system it is worth trying other systems. There are two distinct phases of crystallization: 1. Nucleation: This is when a solid first starts to precipitate from a solu-tion. The formation of a crystalline solid rather than oil or wax can be highly solvent dependent, so the correct choice of solvent is crucial. 2. Crystal growth: This is the second phase of crystallization. In gen-eral, the slower the rate of crystallization the larger the size of the crystals formed.

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  eBook - ePub

  Fundamentals of Fragrance Chemistry

  • Charles S. Sell(Author)
  • 2019(Publication Date)
  • Wiley-VCH

    (Publisher)

  5 Separation and Purification

  In order to analyse and manipulate materials, it is important to be able to isolate them from mixtures and obtain them in pure form. The various methods by which Purification can be achieved will be described in this chapter. In fragrance chemistry, the two principal properties we use to achieve separation of materials are volatility and solubility. The volatility of a material is its ability to become a gas rather than a solid or liquid. Distillation is a Purification process that relies on volatility. Crystallisation, solvent extraction, and chromatography rely on a material's solubility.

  Distillation

  In the simplest application of distillation, liquids

  can be separated from the solids dissolved in them by heating the liquid above its boiling point so that it is removed as vapour and then condensing the vapour by contact with a cold surface so that it returns to the liquid state. An example of this might be the separation of water from brine. The liquid that distils is known as the distillate

  , and the material that remains in the still pot is known as the residue. So, in the case of brine distillation, the distillate would be pure water, and the residue would be salt. The simplest form of still therefore comprises a pot (in which the liquid to be distilled is heated and evaporated), a condenser (in which the vapour is cooled to return it to the liquid state), and a

  receiver (in which the distillate is collected). Figure

  5.1

  shows a drawing of such a still.

  Figure 5.1

  A simple still.

  The heat source could be an open flame or an electrical heater. Gas and electrical heaters sometimes use water or oil as a heat transfer medium. The heat source is applied to a thermally stable oil or to water, and the heated liquid is then brought into contact with the outer surface of the still pot. This

  system has the advantage that localised overheating (or hot spots) is avoided. Hot spots on the pot surface can lead to uneven boiling, generating mechanical shocks, and to degradation of material in the pot. The condenser may be air‐cooled or, more often, have a supply of cold water running around it as shown

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  Water Purification Techniques

  • (Author)
  • 2014(Publication Date)
  • University Publications

    (Publisher)

  ________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Water Purification Water Purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water) but water Purification may also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacology, chemical and industrial appli-cations. In general the methods used include physical processes such as filtration and sedimentation, biological processes such as slow sand filters or activated sludge, chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light. The Purification process of water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi; and a range of dissolved and particulate material derived from the surfaces that water may have made contact with after falling as rain. The standards for drinking water quality are typically set by governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the use that is to be made of the water. It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 1800s – must now be tested before determining what kind of treatment, if any, is needed. Chemical analysis, while expensive, is the only way to obtain the information necessary for deciding on the appropriate method of Purification.

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  Practical Process Research and Development

  • Neal G. Anderson(Author)
  • 2000(Publication Date)
  • Academic Press

    (Publisher)

  C H A P T E R 1 1 Tools for Purifying the Product: Column Chromatography, Crystallization and Reslurrying 223 I. INTRODUCTION The chemist has many options for purifying and isolating intermediates and final products.The operations preferred on scale differ from those routinely used in the laboratory, as discussed in Chapter 1. Deferred Purification by telescoping should not be overlooked as a productivity-boosting option. Purification may include extractions and polish filtration performed as part of work-up (Chapter 10) and subsequent chromatography, crystallization, and/or reslurrying. Liquid products may be purified and isolated by distillation. Considering the drawbacks of chro-matography on scale, chromatographic Purifications are generally used only when reaction optimization and non-chromatographic means of Purification prove inadequate to prepare high-quality product. Distillation on scale usually requires specialized equipment and is limited to relatively low molecular weight com-pounds that do not decompose during heating. Isolation of solid intermediates and final product is often achieved by crystal-lization. Intermediates may be upgraded by crystallization, decreasing the burden on the Purification of the final product. Under controlled conditions, crystalliza-tion generally provides the best Purification of a product, and it may be essential for preparing API of the desired purity and polymorphic state. As crystallization on scale can be labor-intensive and equipment-intensive, care must be taken to institute a rugged crystallization process. The following sections discuss chromatography on scale first, as compounds are usually crystallized after chromatographic Purification. The theory of crystal-lization is described, followed by a discussion on morphic states and salt selection. Guidelines are presented to predict how readily a crystallization and isolation process can be performed on scale.

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