Picric acid, complexes

Picric acid complexes are useful for isolation and characterization. A complex can be split by extraction of a benzene solution with ammonium hydroxide or by chromatography on alumina, which retains the picric acid. 

Vasitiades J. Reaction of alkaline sodium picrate with creatinine 1. Kinetics and mechanism of formation of the non creatinine picric acid complex. Clin Chem 1976 22 1664-71. 

Forms molecular addn products with nitro compounds. Picric acid complex, mp 139 sym.trinitrobenzene complex, mp 164" trinitrotoluene complex, mp 162". 

Figure 11 Intermolecular contacts shorter than EvdW in the crystal structure of the d-nitropyiidine-AT-oxide-picric acid complex (a) O-H- 0 and C-H- - -O H-bonds and (b) nn md n TV k) CT interactions. (Reproduced by permission from Bertolasi et al, 2011 American Chemical Society, 2011).

Ci8H2oN80ig, Carbamoylcholine picrate-picric acid complex, 41B, 7... 

Picrates, Picric acid combines with amines to yield molecular compounds (picrates), which usually possess characteristic melting points. Most picrates have the composition 1 mol amine 1 mol picric acid. The picrates of the amines, particularly of the more basic ones, are generally more stable than the molecular complexes formed between picric acid and the hydrocarbons (compare Section IV,9,1). 

The achiral triene chain of (a//-rrans-)-3-demethyl-famesic ester as well as its (6-cis-)-isoiner cyclize in the presence of acids to give the decalol derivative with four chirai centres whose relative configuration is well defined (P.A. Stadler, 1957 A. Escherunoser, 1959 W.S. Johnson, 1968, 1976). A monocyclic diene is formed as an intermediate (G. Stork, 1955). With more complicated 1,5-polyenes, such as squalene, oily mixtures of various cycliz-ation products are obtained. The 18,19-glycol of squalene 2,3-oxide, however, cyclized in modest yield with picric acid catalysis to give a complex tetracyclic natural product with nine chiral centres. Picric acid acts as a protic acid of medium strength whose conjugated base is non-nucleophilic. Such acids activate oxygen functions selectively (K.B. Sharpless, 1970). 

In this experiment the method of continuous variations is used to determine the stoichiometry and equilibrium constant for the organic complex of 3-aminopyridine with picric acid in CHCI3, and the inorganic complex of Fe +with salicylic acid. 

Presumably perchloric acid oxidizes the steroids at ring A and these then form charge transfer complexes with picric acid. 

The composition and nature of the charge-transfer complexes of 2-quinoxalina-mine with tetrachlorobenzoquinone (chloranil), tetrabromobenzoquinone (bromanil), 1,3,5-trinitrobenzen, and picric acid have been determined likewise those of 2,3-quinoxalinediamine with chloranil and bromanil. 

Complexes in Which the Acceptor Is an Organic Molecule. Picric acid, 1,3,5-trinitrobenzene, and similar polynitro compounds are the most important of these. Picric acid forms addition compounds with many aromatic hydro... 

Behrend C, K Heesche-Wagner (1999) Formation of hydride-Meisenheimer complexes of picric acid (2,4,6-trinitrophenol) and 2,4-dinitrophenol during mineralization of picric acid by Nocardioides sp. strain CB 22-2. Appl Environ Microbiol 65 1372-1377. 

Picric acid, in common with several other polynitrophenols, is an explosive material in its own right and is usually stored as a water-wet paste. Several dust explosions of dry material have been reported [1]. It forms salts with many metals, some of which (lead, mercury, copper or zinc) are rather sensitive to heat, friction or impact. The salts with ammonia and amines, and the molecular complexes with aromatic hydrocarbons, etc. are, in general, not so sensitive [2], Contact of picric acid with concrete floors may form the friction-sensitive calcium salt [3], Contact of molten picric acid with metallic zinc or lead forms the metal picrates which can detonate the acid. Picrates of lead, iron, zinc, nickel, copper, etc. should be considered dangerously sensitive. Dry picric acid has little effect on these metals at ambient temperature. Picric acid of sufficient purity is of the same order of stability as TNT, and is not considered unduly hazardous in regard to sensitivity [4], Details of handling and disposal procedures have been collected and summarised [5],... 

The mixture is then chilled in an ice bath for at least 3 hours, and the olive-brown precipitate of the sparingly soluble copper complex of imidazole derivatives is filtered. The product is washed with about 500 ml. of cold water, suspended while moist (Note 4) in 11. of water, and rendered just acid to litmus by the addition of concentrated hydrochloric acid (about 40 ml.). Hydrogen sulfide is then passed into the suspension, with frequent shaking, until precipitation of the copper is complete (2-3 hours). The precipitate is filtered and extracted with 500 ml. of hot water in two or three portions. The clear, light brown to reddish brown filtrate and washings are boiled for 15 minutes, and then 60 g. (0.26 mole) of picric acid is added with stirring heating is continued until solution is complete. 

Some complications arise from the presence of proton donor-acceptor interactions134 when the donor is a protic amine. The separate evaluation of the two kinds of interactions may be a difficult problem. Similarly, if the electron acceptor is also a proton donor, the overlapping of salification and complexation processes makes the separate investigation of the interactions very difficult. This is the case in the complexes between amines and picric acid or other related phenols. For complexes of 2,4,6-trinitro-3-hydroxypyridine135 and... 

We have mentioned above the prevalence of chromoisomeric effects in two-component systems forming solid charge-transfer complexes. This was studied first by Hertel (120) and labeled by him complex isomerism. In a system such as picric acid with an aromatic amine, there are a variety of structural possibilities. There will probably be intermolecular hydrogen bonds, which are associated with short lateral contacts between the near-planar molecules. In addition, there... 

In the dihydrochloride (602), the second molecule of acid is not firmly bound because of protonation of the second basic site by internal hydrogen bond formation. This would suggest that in the dipicrate, one mole of picric acid participates in salt formation, and that the second mole of picric acid is added to the hydrogen-bonded cation (LXI) forming a molecular complex. The existence of a monopicrate might thus serve to point out structures with steric inhibition of hydrogen bonding. 

The interaction of phenylbiguanide and ethyl p-ethoxypropionate in the presence of sodium methoxide yields a readily dissociable molecular complex of the expected guanamine and phenylbiguanide 486) (CLXIX). Aqueous picric acid cleaves the complex into the picrates of its constituents. However, the complex is not formed from the pre-formed 2- -ethoxyethyl-6-phenylguanamine (or its methyl analogue) and phenyl-biguanide in methanol or acetonitrile, and its nature is not completely understood (see also ref. 605). 

Examples of such charge-transfer complexes include the complex formed between a metal ion and a -n orbital of a double bond or an aromatic system , the complex formed between polynitro aromatics (such as picric acid) and other w-orbital-containing molecules, and complexes of I2 and Br2 with amines, ketones, aromatics, etc ° Phenols and quinones also form charge-transfer complexes ... 

The formation of unusually light colored charge-transfer complexes of 8 with both picric acid and trinitrobenzene may be attributed to the decrease of the interaction between the donor and acceptor molecules due to the curvature of the former. ... 

The two starting components were packed into a glass capillary from opposite ends until they met in the centre. A coloured reaction product was observed visually after 7 to 10 min at the reactant interface. As time progressed, the product interface was observed to advance in the direction of the picric acid reactant. Further study of this reaction supported a vapour diffusion mechanism, bolstered in part by the observation that complexation proceeds even if a small gap of space exists between the two reactants [12]. The nature of the complex was investigated in additional work, whereby it was proposed that a donor/acceptor 71-complex was produced [13]. A crystal structure confirming this deduction was later published [14]. 

The LFP studies of the reaction of the A-methyl-A-4-biphenylylnitrenium ion with a series of arenes showed that no detectable intermediate formed in these reactions. The rate constants of these reactions correlated neither with the oxidation potentials of the traps (as would be expected were the initial step electron transfer) nor with the basicity of these traps (a proxy for their susceptibility toward direct formation of the sigma complex). Instead, a good correlation of these rate constants was found with the ability of the traps to form n complexes with picric acid (Fig. 13.68). On this basis, it was concluded the initial step in these reactions was the rapid formation of a ti complex (140) between the nitrenium ion (138) and the arene (139). This was followed by a-complex formation and tautomerization to give adducts, or a relatively slow homolytic dissociation to give (ultimately) the parent amine. 

In an earlier investigation by the authors (2) (3-cyclodextrin complexes with poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) capped with picric acid, (I), were prepared that formed complexes with nucleic acids and were used in gene therapy. 

---