Solvent The dissolving medium

Summary A solution is a homogeneous mixture composed of a solvent and one or more solutes. The solvent is the substance that acts as the dissolving medium and is normally present in the greatest amount. Commonly the solvent is a liquid, but it doesn t have to be. Our atmosphere is a solution with nitrogen as the solvent it is the gas present in the largest amount (79%). Many times you will be dealing with a solution in which water is the solvent, an aqueous solution. The solute is the substance that the solvent dissolves and is normally present in the smaller amount. You may have more than one solute in a solution. For example, if you dissolved table salt (sodium chloride) and table sugar (sucrose) in water, you would have one solvent (water) and two solutes (sodium chloride and sucrose). 

However, before we can understand solution reactions, we need to discuss the nature of solutions in which water is the dissolving medium, or solvent. These solutions are called aqueous solutions. In this chapter we will... 

A solute is the substance being dissolved. The solvent is the dissolving medium. 

Antibonding molecular orbital an orbital higher in energy than the atomic orbitals of which it is composed. (14.2) Aqueous solution a solution in which water is the dissolving medium or solvent. (4)... 

Cell solutions, ocean water, and steel may appear quite dissimilar, but they share certain characteristics. In Chapter 3, you learned that solutions are homogeneous mixtures containing two or more substances called the solute and the solvent. The solute is the substance that dissolves. The solvent is the dissolving medium. When you look at a solution, it is not possible to distinguish the solute from the solvent. 

AMPS is a water-soluble monomer it is also soluble in polar organic solvents such as methanol, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). MPDMA is soluble in similar polar solvents. Because of the solubility characteristics of these two species, the reactions (that is, the formation of the ion pairs) were conducted in water, methanol, or DMF. The product, MPDMA AMPS, was very hygroscopic and apparently had a tendency to polymerize spontaneously during the course of isolation (solvent stripping and precipitation by non-solvents). The preferred medium for preparation was found to be anhydrous THF which also had been used for other ionic monomer pairs (13). In addition, a slight excess of MPDMA was used to ensure complete reaction of AMPS. The excess base, MPDMA, was removed using cold THF (which did not dissolve the product). 

Flowever, before we can understand solution reactions, we need to discuss the nature of solutions in which water is the dissolving medium, ox solvent. These solutions are called aqueous solutions. In this chapter we will study the nature of materials after they are dissolved in water and various types of reactions that occur among these substances. You will see that the procedures developed in Chapter 3 to deal with chemical reactions work very well for reactions that take place in aqueous solutions. To understand the types of reactions that occur in aqueous solutions, we must first explore the types of species present. This requires an understanding of the nature of water. 

Aqueous solution a solution in which water is the dissolving medium or solvent. (4)... 

INTRODUCTION AND SECTION 4.1 Solutions in which water is the dissolving medium are called aqueous solutions. The component of the solution that is present in the greatest quantity is the solvent. The other components are solutes. 

Selection of solvents. The choice of solvent will naturally depend in the first place upon the solubility relations of the substance. If this is already in solution, for example, as an extract, it is usually evaporated to dryness under reduced pressure and then dissolved in a suitable medium the solution must be dilute since crystallisation in the column must be avoided. The solvents generally employed possess boiling points between 40° and 85°. The most widely used medium is light petroleum (b.p. not above 80°) others are cycZohexane, carbon disulphide, benzene, chloroform, carbon tetrachloride, methylene chloride, ethyl acetate, ethyl alcohol, acetone, ether and acetic acid. 

An alternative polymerization process utilizes a slurry of calcium chloride in NMP as the polymerization medium. The solubiHty of calcium chloride is only 6% at 20°C however, the salt continues to dissolve as conversion of monomers to polymer proceeds and calcium chloride/polyamide complexes are formed. Polymer molecular weight is further increased by the addition of /V, /V- dim ethyl a n i1 in e as an acid acceptor. This solvent system produces fiber-forming polymer of molecular weights comparable to that formed in HMPA/NMP. 

Organic Dye Lasers. Organic dye lasers represent the only weU-developed laser type in which the active medium is a Hquid (39,40). The laser materials are dyestuffs, of which a common example is rhodamine 6G [989-38-8]. The dye is dissolved in very low concentration in a solvent such as methyl alcohol [67-56-17, CH OH. Only small amounts of dye are needed to produce a considerable effect on the optical properties of the solution. 

Producing a polystyrene (PS)-DVB copolymer of increasing porosity has been accomplished by dissolving 50-80% styrene, 10-50% divinylbenzene, and 30-70% of an inert organic liquid. Toluene is a solvent for the monomer but is a nonsolvent for the polymerized polymer. The monomer solution is then incorporated into water to form a dispersion of oil droplets followed by the polymerization of the suspended oil droplets from the aqueous medium into the polymer (21). 

The crude product separates as a solid from the reaction medium and is recovered by filtration, and it is then washed thoroughly with ether and dissolved in 350 ml 1 N HCI. Then, approximately 250 ml of the aqueous solvent is removed with a rotary evaporator and the evaporation residue combined with 125 ml methanol and filtered through decolorizing charcoal. The product is precipitated as the HCI salt by the addition of 7 parts of acetone. The resulting crystalline material is removed by filtration dried at 40°C with vacuum, and has a melting point of about 242°C and Is used without further purification. 

After evaporation of the solvent, the solid residue consists of 5-(2-chlorobenzyl)-thieno[3,2-cl -pyridinium chloride which melts at 166°C (derivative n°30). This compound is taken up into a solution comprising ethanol (300 ml) and water (100 ml). Sodium borohydride (NaBH4) (20 g) is added portionwise to the solution maintained at room temperature. The reaction medium is maintained under constant stirring during 1 2 hours and is then evaporated. The residue is taken up into water and made acidic with concentrated hydrochloric acid to destroy the excess reducing agent. The mixture is then made alkaline with ammonia and extracted with ether. The ether solution is washed with water, dried and evaporated. The oily residue is dissolved in isopropanol (50 ml) and hydrochloric acid in ethanol solution is then added thereto. 

---