Sodium reaction + halogen atoms

We say that the hydroxyl group has been displaced, and the halogen atom substituted for it. You can see that the group CH3CH2— has remained intact in all of these reactions. Indeed, this group has appeared in most of our discussion so far, sometimes attached to oxygen (as in ethanol and sodium ethoxide), sometimes attached to other atoms (as in the ethyl halides). You will recall that earlier we became acquainted... 

The enhanced reactivity of 5-halogeno-l,2,4-thiadiazoles over 3-halogeno-l,2,4-thiadiazoles has been mentioned before (see Section 5.08.7.1). Nucleophilic substitution at this center is a common route to other 1,2,4-thiadiazoles, including 5-hydroxy, alkoxy, mercapto, alkylthio, amino, sulfonamido, hydrazino, hydroxylamino, and azido derivatives. Halogens in the 3-position of 1,2,4-thiadiazoles are inert toward most nucleophilic reagents, but displacement of the 3-halogen atom can be achieved by reaction with sodium alkoxide in the appropriate alcohol <1996CHEC-II(4)307>. 

If one takes out of this list the polyhalomethanes and tries to understand what the chemistry is about, certainly a simple-minded view is that this is simply a halogen atom abstraction reaction such as one finds in a gas phase reaction, like sodium atom with organic halides. There is a linear free energy correlation in that the logarithms of the rate constants bear a linear relation to one another. 

The reaction can be rationalized as involving an E2 fragmentative attack by the teUuride anion at the halogen atom. Sodium hydrogen tellnride (method B) requires a shorter reaction time than sodinm tellnride (method A), the 2-bromoalkyl esters reacting very rapidly. Sodinm hydrogen selenide reacts similarly but more slowly. ... 

Free radical attack at the pyridine ring is noted for its low selectivity and substituents have little effect. Arylation takes place at all three positions, but halogen atoms preferentially attack the a-, and alkyl radicals the a- and y-positions. Metals such as sodium and zinc transfer a single electron to pyridine to form anion radicals. These can dimerize by reaction at the a- or y-position to yield dipyridyls by loss of hydride ion. Thus, reduction of pyridine by chemical and catalytic means is easier than reduction of benzene. 

Owing to a sufficient reactivity of the secondary halogen atoms towards nucleophiles, the telomers 421 (n = 1) have also been transformed286 into tetroses. Reaction of 430 with sodium cyanide, induced by a phase-transfer catalyst, afforded trans-438 and ci.s-439 nitriles in... 

One of the main products in each case was the expected 5,6-dihy-droxy-7-iodoindole,70,109,119, 1B1,166 which was invariably accompanied by some of the corresponding deiodinated product.1BB (The elimination of the halogen atom in reactions of this type has been referred to previously.109) Reduction of 7-iodoadrenochrome (12) with Na2S204 gives, besides 5,6-dihydroxy-7-iodo-V-methylindole (55) and 5,6-dihydroxy-iV-methylindole (28), the sodium bisulfite... 

Reaction VR (a) Action of Sodium on Halogen Compounds (Wiirtz, Fittig, and Freund). (A., 131, 303.)—The application of this reaction to the synthesis of paraffins by Wiirtz was of great importance to chemical theory, as it afforded strong evidence of the chain linking of carbon atoms, and enabled the structure of many hydrocarbons to be determined by their syntheses. 

The reactions of sodium and potassium atoms with halogens, nitrogen oxides... 

For poly silanes made by Wurtz reaction, the presence of functional groups in polysilane polymers is limited by the vigorous conditions of the sodium condensation reaction. Any substituents that react with molten sodium metal must therefore be introduced after the polymer is synthesized. Halogen atoms can be introduced into alkenylpolysilanes by HBr or HC1 addition reactions, as shown for the 3-cyclohexenyl-ethyl polymers in equation (21).37 Chlorine atoms have also been introduced into arylpolysilanes by chloromethylation, in which -CH2C1 groups are substituted onto phenyl rings in the polymer.38... 

Sodium and alcohol can only be used to remove a halogen atom from the 5-position in 1-arylpyrazoles the ring is reduced to a pyrazoline during the reaction.550,582,663 The halogen may be removed from... 

The enthalpy of formation of the azide radical is 467 SkJmoR. The spin-allowed dissociation to N( D) and N2(X 1 +) is endoergic by 225kJmol, the dissociation enthalpy to N( S) - -N2(X i +) is 0.5 IkJmol. The azide radical is only stable because this spin-forbidden decomposition pathway has an appreciable energy barrier. In aqueous solution, it primarily exists as a monomer, in contrast to other halide or pseudohaUde radicals that exist as the less reactive dimers (e. g. Brs (SCN)2 ). Reaction ofthe azide radical with halogen atoms or other small molecules hke O2, NO, CO, and CO2 produces molecules in electronically excited states because of propensity rules, which can be used for chemically pumped lasers. The azide ion is also formed during high-pressure photolysis of sodium azide. 

Derivatives of phenol or aniline can be oxidized to quinones, the yield and ease of oxidation depending on the substituents. If an amino or hydroxyl group is in the para position, the reaction proceeds readily, as illustrated by the synthesis of quinone from hydroquinone by oxidation with a sodium chlorate-vanadium pentoxide mixture (5>6%) or with chromic-sulfuric acid mixture (92%). A para halogen atom usually has a favorable effect. Any group in the para position is eliminated or oxidized. o-Quinones are usually prepared from the corresponding catechols. A survey of procedures for the synthesis of benzoquinones by oxidation has been made. ... 

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