Lawrence B. Ebert

Graphite Intercalation Compounds

Publisher Summary Twenty years ago, Walter Rudorff wrote a review for the series entitled “Graphite Intercalation Compounds” (R1). It was one of the four definitive articles to come out in 1959 and 1960 (HI, C1, U1), a period of intense activity in graphite research. One have now again reached the “fever pitch,” with not only the appearance of several new articles (E l , H2, W1), but also the convening of the first international conference dedicated exclusively to graphite compounds (H3 ). In the following, one shall concentrate on the work performed between 1974 and the present. The interlayer voids are frequently attacked to yield a periodic sequence of filled and empty spaces. The stage of a compound is defined as the ratio of host layers to guest layers, so that a first-stage compound, in which every interlayer void is filled, is the most concentrated. Historically, compounds of graphite have been placed in three categories, depending on the strength of interaction between the reacting species and graphite.

Magnetic resonance of intercalation compounds of graphite: Questions of ionicity and mobility of inserted species

Abstract Graphite will react at room temperature with Lewis acids as PF 5 and BF 3 in the presence of the oxidant C1F to form intercalation compounds containing closed-shell anions. In the case of “C 16 BF 4 ”, the chemical shifts of both 11 B and 19 F nuclear magnetic resonances point to the existence of BF − 4 , rather than the initial BF 3 , within the graphite planes. The existence of second order quadrupolar coupling of the 11 B resonance suggests, however, possible hybrid BF 3 BF − 4 character, as in B 2 F − 7 , a known dimeric anion of BF 4 and BF 3 . NMR results on 19 F and 31 P in the two compounds “C 14 PF 6 ” and “C 28 PF 6 ” support this hypothesis, as “C 28 PF 6 ” shows only the presence of PF − 6 , but the more concentrated “C 14 PF 6 ” shows composite PF 5 PF − 6 character. Our claim for intercalated anions in these systems is reinforced both by radical cation-type signals in the ESR and by deshielding effects in the 13 C NMR. The narrow linewidths of the nuclear magnetic resonance absorptions of the intercalated species are suggestive of “liquid-like” behavior.

X-RAY DIFFRACTION OF N-PARAFFINS AND STACKED AROMATIC MOLECULES: INSIGHTS INTO THE STRUCTURE OF PETROLEUM ASPHALTENES

ABSTRACT X-ray diffraction investigation of normal paraffins and Debye internal interference calculations on stacks of aromatic molecules are used to make inferences about the structure of petroleum asphaltenes. The gamma band, a broad peak near 4.5 A, is associated with weakly ordered paraffins. Stacks of aromatic molecules can give rise to diffraction peaks at d value higher than that of the “(002)” line. X-ray diffraction of the liquids n-hexadecane, decalin, perhydro-fluorene, 1,3 dimethyladamantane, and 1-methyl naphthalene confirms the above insights and demonstrates that diffraction can distinguish among the organic structural types “paraffinic,” “naphthenic,” and “aromatic.”

APPLICATIONS OF INTERCALATION COMPOUNDS

This article describes the applications of intercalation compounds that are either commercially practiced or under active development. The range of compounds discussed will be somewhat broader than those formed by an intercalation reaction, including where appropriate many insertion type reactions that do not strictly fit the criteria of intercalation; that is, of ready reversibility and minor structural changes of the host lattice matrix.

COMMENT ON THE STUDY OF ASPHALTENES BY X-RAY DIFFRACTION

Abstract In the x-ray diffraction of carbonaceous materials, there is no logical reason to assume an interrelation between the intensity of the (002) peak, reflecting intermolecular “stacking” order of aromatic planes, and the fractional aromaticity fa measured by carbon nuclear magnetic resonance. Approaches to the calculation of a diffraction-based aromaticity f002 by comparing the intensity of the (002) peak to that of the γ-band at 450 pm, reflecting intermolecular order of saturated chain hydrocarbons, are fundamentally flawed. The use of diffraction linewidth data for peaks near 210 pm (“(100)”) and near 120 pm (“(110)”) to infer an aromatic diameter has difficulties in systems containing hydroaromatic molecules (e.g., tetralin) because the naphthenic moiety contributes to diffraction peaks in the 210 and 120 pm regions.

The disruption of aromatic stacking order in mesophase petroleum coke via reductive alkylation

Abstract The thermolysis of a 510° C vacuum residuum of petroleum under hydrogen can lead to an insoluble coke material of correlation length in the direction of aromatic stacking (L c ) of 7.3 nm, which is more than 3 times greater than that typically found for coals of anthracite rank. In spite of this high degree of stacking order, the coke material can be solubilized via the technique of reductive alkylation. The coke is combined with tetrahydrofuran and potassium metal, and the aromatic “molecules” of the coke form solubilized anions (K° consumption 5–6 mmol/gram). These anions react with alkyl iodides to form alkylated aromatic adducts, of vapor pressure osmometry molecular weight ca. 1000 gram/mole and showing only weak intermolecular paraffin interactions in X-ray diffraction. Thus, a high degree of aromatic stacking, as manifested by a narrow (002) peak in diffraction, does not imply that the material is refractory; the chemical significance of such aromatic-aromatic interactions is currently of interest to those studying both carbon fibers and coal conversion. Heteronuclear correlated 1 H/1b 13 C NMR is used to elucidate the detailed chemistry of the disruption of aromatic stacking.

Chemistry of Engine Combustion Deposits: Literature Review

As an autombile engine runs, its fuel quality requirements, as measured by the octane number of the fuel needed to inhibit knocking, may change in time. Historically, this phenomenon is referred to as the “ORI” problem, standing for octane requirement increase.

More on the reaction of graphite/potassium with water

Abstract The first stage intercalation compound of graphite with K°, C 8 K, will react with water at room temperature to yield a solid product containing graphite inserted with potassium cations and water molecules. Temperature-variant 1 H NMR shows that both T 1 and T 2 decrease as temperature decreases from 298 K to 213 K (T 1 > T 2 at these temperatures) with an activation energy of 0.25 eV. Starting with a C 8 K D 2 O product, one can isotopically exchange with H 2 O to yield a product with 17% H 2 O after 48 hours at room temperature, showing the inserted species are not kinetically “encapsulated.” X-ray diffraction, thermogravimetric analysis, and nuclear magnetic resonance are used to distinguish the graphite compound from a mixture of graphite and hydrates of potassium hydroxide.

Reductive alkylation of petroleum residua using potassium metal and tetrahydrofuran at room temperature

Abstract Two petroleum residua from the same source, one of distillation cutpoint 510 °C (950 °F) and one of cutpoint 704 °C (1300 °F), were placed in THF and reacted with potassium metal at room temperature for 24 h. The consumption of K metal was 4.1–5.0 mmol K (g resid) 2 for the 510 °C −1 resid, and 3.7–3.9 m mol g −1 for the 704 °C + resid. Although both resids showed a (002) peak in X-ray diffraction, alkylation of the resid anions with either methyl or hexyl iodides removed this feature, proving that reductive alkylation does disrupt the stacking of aromatic entities. Sequential reductive alkylations were performed on the 510 °C + resid, first with CD 3 I and second with 13 C-enriched CH 3 I. N.m.r. shows that CD 3 S thioethers formed after the first reductive alkylation are completely destroyed after the second reductive alkylation, but that new 13 CH 3 S thioethers are formed after the second reductive alkylation. This behaviour is completely unlike that known for dibenzothiophene under identical chemical conditions.

The reaction of iodine oxide pentafluoride and rhenium oxide pentafluoride with graphite

Abstract IOF 5 intercalates into graphite accompanied by partial oxygenation of the graphite host. The intercalated species was identified by 19 F nmr spectroscopy. Oxygenation of the graphite was established by analyses of the gaseous reaction products. Intercalation of ReOF 5 into graphite is accompanied by liberation of large amounts of ReF 6 and traces of COF 2 and COF 2 . The oxygenation of the graphite was established by weight increase. The stoichiometry of the reactions and physical measurements indicated that the intercalated species is ReF 4 together with varying amounts of ReF 6 . The formation of these fluorides from ReOF 5 can be explained in terms of an intermediate formation of ReF 5 followed by its disproportionation.