Urethans hydroxy compounds

Another fluorescent pigment class (23) is based on a urethane-type resin the primary raw materials are isocyanates, amines, and hydroxy compounds. 

As explained in Chapter 1, the urethane group is the product of the reaction of a hydroxy compound with an isocyanate group (Reaction 4.8). This reaction occurs by step kinetics, yet is usually an addition process since no small molecule is lost as the reaction proceeds. 

Polyurethanes are macromolecules in which the constitutional repeating units (CRUs) are coupled with one another through urethane (oxycarbonylamino) groups. They are prepared almost exclusively by stepwise addition polymerization reactions of di- or polyfunctional hydroxy compounds with di- or polyfunctional isocyanates ... 

The instability of the 3-hydroxymethylindoles over a wide pH range results in the lack of success in acetylation of the hydroxy compound and also in the failure to hydrolyze the acetoxymethylindole without conversion into the bis(3-indolyl)methane (79HC(25-3)l). In contrast with the 3-isomer, 2-hydroxymethylindoles are stable to bases, but are polymerized by acids (79HC(25-3)l). Similarly, it is possible to convert 3-hydroxymethylpyrroles into their acetates and methyl ethers under basic conditions, and reaction with isocyanates yields the expected urethanes (79JMC977). Under acidic conditions, however, they produce the bis(3-pyrrolyl)methanes (B-77MI30504). 

Urethanes (or carbamate esters) are compounds that are the product of the reaction of isocyanates -N=C=0 with a hydroxy compound. This reaction can be written as follows ... 

Characteriuitioii oflundertd tkohots and plutwls The reagent readily converts hindered hydroxy compounds into urethanes and hence is useful for the preparation of characterizing derivatives. Thus in the reaction with t-butanol in toluene (0.01 M solution) at 0°, titration after 1 min. indicated that only a negligible amount of... 

Carbonyl azides react with alcoholic hydroxy compounds to form the corresponding urethanes. In the same manner, ferrocenoyl azide, and 3-fe-rrocenylpropionyl azide can derivatized, hydroxy-steroids and the resultant derivatives are determined electrochemically by LC with the detection limits at subpicomole levels. 2-[2-(Azidocarbonyl)ethyl]-3-methyl-1,4-naphthoquinone (AMQ) reacts with primary and secondary alcohols to produce carbamic acid derivatives and is used in LC with BCD and FL detections. 7-Methoxycoumarin-4-carbonyl azide (7-MC-4-CON3) and 3,4-dihydro-6,7-dimethoxy-4-methyl-3-oxoquinoxaline-2-carbonyl azide (DMEQ-CON3) are also applied to LC with FL detection as precolumn reagents. 

In simplest terms, the raw materials for urethanes consist of compounds having two or more isocyanate groups and compounds having two or more hydroxyl groups. These hydroxy compounds, commonly called polyols, are most often polyethers and polyesters, although some other materials are also encountered. 

The basic reaction involved in the formulation of PU is between hydroxy compounds and isocyanates. The first record of this reaction was made by Wurtz and Hoffmann in 1848. Commercially significant advances did not occur until 1937, when 0. Bayer of Germany developed diisocyanate. Bayer and co-workers continued the development of polyester-based urethane polymers as nylon substitutes in the 1940-45 time period. Polyester toluene-diisocyanate (TDI) foams became commercially available in the United States in 1952-53. Two further developments occurred that allowed the use of PU foam to reach the present level. The first of these was the development of polyether polyol and the subsequent "one-shot" foaming process. Rigid polyether-based foams were available in 1957. The second development was the incorporation of halocarbons as blowing agents in 1958. 

Recently, N,N -disubstituted-5-acyliminoimidazolidinediones (22) have been reported as blocking agents for hydroxy compounds. " These materials were used to prepare blocked polyols which, when formulated with isocyanates, yielded cured urethanes upon heating to above 140°C. This apparently occurs by the thermal dissociation of the blocked complex (23) into free alcohol and starting imidazolidinedione (22), as outlined in Scheme 2,... 

The urethane group results from the interaction of an isocyanate and a hydroxy compound ... 

The isothiocyanates can react further, e. g., with hydroxy compounds or thiols, to form thio-urethanes or dithiourethanes. In the presence of amines, thioureas result while hydrolysis yields the corresponding amines and releases CO2 and H2S ... 

The urethane oils and urethane alkyds constitute about 50% of the total products of alkyds. They correspond in composition to the conventional air drying alkyds discussed earlier, the only difference being that the dibasic acid (phthalic acid) used in the case of air drying alkyds is replaced by an isocyanates (R-N = C = O). The most common isocyanate used is toluene diisocyanate (abbreviated as T.D.I.). The T.D.I. reacts with an active hydrogen atom obtained from hydroxy containing compounds, such as polyethers and vegetable oils. The performance depends upon the characteristics of isocyanate and hydroxy compound used. They do not react with moisture. 

A large number of polymeric compounds have been investigated, but most modem propellants utilize prepolymers that ate hydroxy-functional polybutadienes (HTPB), carboxy-functional polybutadienes (CTPB), or a family of polyethylene oxides (PEGs) to form urethanes. Typical cure reactions... 

Preliminary indication of the presence of a phenol ester may be obtained by heating the compound with soda-lime esters of phenols and also aromatic hydroxy-acids usually give the phenol. (Likewise amides, imides, nitriles, substituted hydrazines, urethanes, etc. afford ammonisu)... 

Such reactions are also possible in vitro, as several mild oxidizing agents are at hand nowadays. Thus, the Dess-Martin periodinane (DMP) [50] has been proven to be a versatile and powerful reagent for the mild oxidation of alcohols to the corresponding carbonyl compounds. In this way, a series of new iodine(V)-mediated reactions has been developed which go far beyond simple alcohol oxidation [51], Ni-colaou and coworkers have developed an effective DM P-mediated domino polycy-clization reaction for converting simple aryl amides, urethanes and ureas to complex phenoxazine-containing polycycles. For example, reaction of the o-hydroxy anilide 7-101 with DMP (2 equiv.) in refluxing benzene under exposure to air led to polycycle 7-103 via 7-102 in a yield of 35 % (Scheme 7.28) [52]. 

Amidoximes (96) react at the hydroxy group with isocyanates or carbamoyl chlorides. The resulting urethanes (105) can be cyclized in boiling acetic anhydride (Scheme 43). A,A-Disubstituted urethanes (106) as well as the A-carbamoyl compounds (108), give oxadiazolinones (107) (Schemes 43 and 44) <63HCA1073>. 

Carbamate esters also produced 2-oxo compounds, e.g., the esters of 3-aminopropanol88 and of 3-halogenopropanol.87 A few compounds have thus been prepared from carbamates, e.g., 20, with an aromatic substituent88 [Eq. (10)] or a heterocyclic one.89 Ethyl 7V-(3-hydroxy-propyl) urethanes cyclize to 2-oxo compounds with sodium methoxide.78 An interesting novel approach was to react an A-(chloromethyl)-carbamate with olefins to yield 2190 [Eq. (11)]. 

The main oligoester chain of these compounds may also include fragments of urethanes, sul-foesters, amides, and others. Along with the end-acryl groups, they may contain other reactive groups, such as carboxylic, allyl, hydroxy lie, etc. 

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