L-selectride is an organoborane. It is used in organic chemistry as a reducing agent, for example in the reduction of a ketone, as part of Overman's synthesis of. Michael Addition. The 1,4-addition (or conjugate addition) of resonance-stabilized carbanions. The Michael Addition is thermodynamically controlled; the reaction. The Chemistry of Nitrogen Compounds Dr David A.Widdowson (10 Lectures) Supporting Texts. Vollhardt and Schore, 2nd Edition Chapters 21 and 26 with some from Chapter 22. Unit One Part 2: naming and functional groups gjr-–- Migration of Chemical Compounds from Packaging Polymers during Microwave, Conventional Heat Treatment, and Storage - Bhunia - 2. Comprehensive Reviews in Food Science and Food Safety. Original Article. Authors. Kanishka Bhunia,Dept. Sablani,Corresponding author. Dept. Chemical compounds that are incorporated within polymeric packaging materials to improve functionality, may interact with food components during processing or storage and migrate into the food. Once these compounds reach a specified limit, food quality and safety may be jeopardized. Possible chemical migrants include plasticizers, antioxidants, thermal stabilizers, slip compounds, and monomers. Chemical migration from food packaging is affected by a number of parameters including the nature and complexity of food, the contact time and temperature of the system, the type of packaging contact layer, and the properties of the migrants. Researchers study the migration of food- packaging compounds by exposing food or food- simulating liquids to conventional and microwave heating and storage conditions, primarily through chromatographic or spectroscopic methods; from these data, they develop kinetic and risk assessment models. This review provides a comprehensive overview of the migration of chemical compounds into food or food simulants exposed to various heat treatments and storage conditions, as well as a discussion of regulatory issues. Introduction. Food Packaging is a rapidly evolving field. Besides keeping foods safe from contamination and retaining the nutritional properties and sensory characteristics of foods, packaging provides additional features that are important to consumers. These include resealability, tamper evidence, and the display of product information, as well as reuse or recycling features. The use of both flexible and rigid polymeric packaging is growing rapidly, and is driven by new developments in bio- plastics, and the desire to reduce the bulk and weight of metal and glass containers. Polymer packaging incorporated with chemical compounds is commonly referred to as plastics. Incorporation of low- molecular- weight chemical compounds improves functional properties of plastics. However, the potential influence these substances on product safety and quality remains in question when amount of these migrating compounds in food exceed their specified limits. The term “migration” refers to the diffusion of substances from a zone of higher concentration (the food- contact layer) to one of a lower concentration (usually the food surface). This process is often influenced by food- packaging interactions (Arvatoyannis and Bosnea 2. Diffusion of chemical substances from polymers is a very complex process, and is dependent on several parameters, such as concentration of substances in packaging film and food, nature of the foods, temperature, and the time period over which duration of contact occurs. About the Cover: The rhodium(III)-catalyzed, redox-neutral coupling reaction of N-acyl ketimines, generated in situ from 3-hydroxyisoindolinones, with various. During the process of diffusion, these compounds enter into another matrix (such as film or food), which changes their concentration in both the packaging and food. Although chemical compound migration is mainly a diffusion- controlled process, it is equally important to consider the mechanism of convection and chemical reactions. The degree of solvent stirring, polymer- solvent partition coefficients, swelling of solvents, and concentration- dependent diffusivity play a key role in the diffusion process (Reid and others 1. For example, in a liquid, viscous, or solid food, diffusivity may change since the interface between plastics and food material would be different in each of these cases. The migration process can be divided into 4 major steps: diffusion of chemical compounds through the polymers, desorption of the diffused molecules from the polymer surface, sorption of the compounds at the plastic–food interface, and desorption of the compounds in the food (Ferrara and others 2. The mass diffusion process is usually governed by Fick's law. The steady state diffusion process indicates no change in concentration over the time (. NA is the steady state flux; Cp is the concentration of migrant in the polymer; Dp is the diffusion coefficient of migrant in polymer. For practical purposes, diffusion and partition coefficients are assumed to be constant. In polymers such as polyethylene (PE) and polypropylene (PP) with low glass transition temperatures (Tg), it can be assumed that migration of substances made from these materials obey Fick's laws (Brandsch and others 2. The partition coefficient (kp) that determines the migration at the polymer- solvent boundary can be written as: Cs is the migrant concentration in food/food simulant/solvent phase. The lower the k. P value, the more the migrant is absorbed into the food from the polymer. When fatty foods come in contact with these polymers, this value is low (k. P < 1); for water, it is very high (k. P > 1. 00. 0) (Piringer 2. However, the coefficients can vary with concentration and time, leading to non- Fickian diffusion, resulting from the solvent penetration- induced swelling phenomenon (Piringer 2. Changes in temperature may influence the partition coefficient, as the solubility of the migrant changes both in the polymer and food phases at equilibrium. The temperature dependence of partition coefficient is also described with the Arrhenius equation (Bastarrachea and others 2. The process of diffusion is also influenced by temperature. The fundamental equation correlating diffusion coefficient and temperature is the Arrhenius type equation (Bastarrachea and others 2. D0 is the pre- exponential factor, E is the activation energy for diffusive molecules, R is the gas constant, and T is the absolute temperature of the system. Several approaches have been carried out to develop a new model for predicting diffusion of compounds, where Dp = f (molecular mass of migrant, absolute temperature). This correlation was developed by Brandsch and others (2. AP=AP. Diffusion in glassy polymers is much slower than in rubbery polymers. The likelihood of monomer and oligomer migration increases when a plastic is exposed to high temperatures during thermal processing or when food is stored for extended periods. Transfer of chemical compounds from plastics into food has raised concerns about the potentially adverse effects of food products on human health. Much of the initial work in this area was conducted in the 1. A susceptor is a lightly metalized polyethylene terephthalate (PET) that absorbs electromagnetic waves such as microwave (MW) radiation, converting this energy to heat, which is then transferred from the susceptor to the food product by conduction, creating localized areas of high temperature on the product surface. These new MW- specific packaging materials facilitated the development of foods such as microwaveable popcorn and required testing of packaging materials under conditions that were completely new to the food industry. To analyze the overall migration (OM) from the food- contact plastic layer, 4 food simulants are most commonly used to simplify testing for regulatory compliance purposes since the simulants are less chemically complex (Grob 2. The simulants recommended for migration testing are: water (simulant A) to represent aqueous foods (p. H > 4. 5); 3% aqueous acetic acid (simulant B) to represent acidic aqueous foods (p. H < 4. 5); 1. 0% aqueous ethanol (simulant C) to simulate alcoholic food products, and olive oil (simulant D) for fatty foods. Recent regulations on food simulants provided by EU 1. Ethanol 1. 0% (v/v) for aqueous food (simulant A); acetic acid 3% (w/v) for acidic food (simulant B); 2. C); for fatty food, 5. D1) and vegetable oil (simulant D2), and lastly, Tenax (PPPO) for dry food (simulant E). However, the U. S. Food and Drug Administration recommends 1. I, II, IVB, VIB, and VIIB in Table 1); 1. VIA, VIC), and food oil, HB3. Miglyol 8. 12 for fatty foods (type III, IVA, V, VIIA, IX). HB3. 07 is a mixture of synthetic triglycerides, and Miglyol 8. HB3. 07 is the product of NATEC, Hamburg, Germany. Miglyol 8. 12 is a fractionated coconut oil that is composed of saturated C8 (5. C1. 0 (3. 0–4. 5%) triglycerides with boiling point range of 2. This product is made by Dynamit Nobel Chemicals, HULS America Inc., Piscataway, NJ. Table 1 shows the classification of types of food and food simulants recommended for FCM (Barnes and others 2. Table 1. Classification of food types and food simulants for food- contact materials recommended by FDA (reproduced from chemical migration and food- contact materials by Barnes and others 2. INonacid, aqueous products; may contain salt, sugar, or both (p. H > 5)Aqueous. IIAcid, aqueous products; may contain salt, sugar, or both, and including oil- in- water emulsions of low- or high- fat content. Acidic. 10% ethanol. IIIAqueous, acid or nonacid products containing free oil or fat; may contain salt, and including water- in- oil emulsions of low- or high- fat content. Fatty. Food oil, HB3. Miglyol 8. 12. IVDairy products and modifications A. Water- in- oil emulsions, high or low fat. Fatty. Food oil, HB3. Miglyol 8. 12 B. Oil- in- water emulsions, high or low fat. Aqueous. 10% ethanol. VLow- moisture fats and oils. Fatty. Food oil, HB3. Miglyol 8. 12. VIBeverages A. Containing up to 8% alcohol. Low alcohol. 10% ethanol B. Nonalcoholic. Aqueous. C. Containing more than 8% alcohol. High alcohol. 50% ethanol. VIIBakery products (other than those under types VIII or IX) A. Moist bakery products with surface containing free fat or oil. Fatty. Food oil, HB3. Miglyol 8. 12 B. Moist bakery products with surface containing no free fat or oil. Aqueous. 10% ethanol. VIIIDry solids with the surface containing no free fat or oil. Dry. Tenax. IXDry solids with the surface containing free fat or oil. Fatty. Food oil, HB3. Miglyol 8. 12. Testing the migration of chemical compounds from food packaging into food simulants involves 2 steps (Castle 1. Comprehensive Organic Synthesis - (Second Edition)Comprehensive Organic Synthesis(Second Edition)Editors- in- Chief: Paul Knochel and Gary A. Molander. ISBN: 9. Copyright . All rights reserved.
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