Selected Reactive Sites Tuned by High Pressure ... - ACS Publications

Subscriber access provided by NEW YORK UNIV

Article

Selected Reactive Sites Tuned by High Pressure: Oligomerization of Solid-State Cyanamide Yuxiang Dai, Kai Wang, Hongsheng Yuan, Xiao Meng, Kun Luo, Dongli Yu, Jing Liu, Xi Zhang, Yuguo Ma, Yongjun Tian, and Bo Zou J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b01105 • Publication Date (Web): 19 May 2015 Downloaded from http://pubs.acs.org on May 23, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Selected Reactive Sites Tuned by High Pressure: Oligomerization of Solid-State Cyanamide ‖

Yuxiang Dai,† Kai Wang,† Hongsheng Yuan,† Xiao Meng,‡ Kun Luo,§ Dongli Yu,§ Jing Liu,‖ Xi ⊥

Zhang,⊥ Yuguo Ma,*,‡ Yongjun Tian,*,§ and Bo Zou,*,† †

‡

State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.

Beijing National Laboratory for Molecular Sciences, Key Lab of Polymer Chemistry & Physics of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China. §

State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.

‖

Beijing Synchrotron Radiation Laboratory, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China. ⊥

Key Laboratory of Organic Optoelectronics & Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, China.

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract We studied high-pressure reaction of solid cyanamide in a diamond anvil cell up to a pressure of 21.7 GPa. The results of in situ high-pressure Raman spectroscopy and angle dispersive X-ray diffraction experiments indicated the occurrence of pressure-induced oligomerization in cyanamide over 13 GPa. The Raman, NMR and UV absorption spectra of recovered samples confirmed that the chemical reaction was irreversible and the high-pressure products contained C=N bonds. Subsequently, results of kinetic studies showed the relation between pressure and the reaction rate. Meanwhile dependence of activation volume with pressure indicated that the steric factors affected the reaction. Additionally, the increase in the amount of C−C bonds of recovered samples was attributed to the change of reactive sites of adjacent C≡N groups. These results suggest that the application of pressure can both tune the reactive sites and the reaction rate to affect oligomerization and even other chemical reactions.

2


Page 2 of 36

Page 3 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Pressure is the most effective physical factor to increase the density of substances. Given that reactive sites in condensed systems can be brought closer by external forces, high pressure can induce and/or accelerate chemical reactions.1,2 As a simple means without any solvent, catalyst, or other environmental impacts, the application of pressure has a unique advantage in green chemistry.3,4 Since progressive experimental facilities have been applied in high-pressure studies, many literatures about chemical reactions affected by extreme pressure have been reported in recent years.5,6 Accordingly, various kinds of molecules containing unsaturated bonds have been subjected

to

extreme

pressure

conditions

for

exploration

of

pressure-induced

polymerization/oligomerization.7-10 The materials prepared by high pressure also have some new properties. For example, dimerization or polymerization of butadiene under high pressure can be switched by different laser irradiation and benzene-derived carbon nanothreads prepared under high pressure has higher stiffness than conventional high-strength polymers.10,11 Some monomer molecules in crystal state are pre-arranged by non-covalent interactions such as hydrogen bonds. These intermolecular interactions can improve the high-pressure products and facilitate pressureinduced reactions.12,13 Meanwhile, studying the efficiency of reactions at different pressures provides kinetic information, which gives insight on reaction equilibrium and growth process of products.1,7,14

Additionally,

in

literatures

regarding

pressure-induced

oligomerization/

polymerization, discussion of reactive sites can improve the understanding of reactive mechanism, which is worth paying more attention.15 Cyanamide, one of the simplest raw materials often used in polymerization reactions, is composed of a NH2 functional group and an unsaturated C≡N functional group in each molecule.16

3

Hydrolysis

can

polymerize

cyanamide


in

aqueous

solutions,

but


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

polymerization/oligomerization of solid cyanamide is barely reported. Cyanamide molecules crystallize into the orthorhombic Pbca structure in solid state. Each cyanamide molecule is linked to four neighboring molecules by two pairs of N−H···N hydrogen bonds. The C≡N groups act as the hydrogen-bond acceptor and the NH2 groups act as the hydrogen-bond donor. Cyanamide molecules are arranged nearly in parallel to the c-axis （in a view along the b-axis） by the three-dimensional N−H···N hydrogen bonds (Figure 1).17 The shortest C···N distance between C≡N groups is 3.38 Å, which avoids polymerization/oligomerization in solid cyanamide at ambient conditions. Elevating pressure is a feasible method to reduce the distance between adjacent C≡N groups and even induce reactions in cyanamide. Investigating the chemical reactions of cyanamide under high pressure can expand the understanding of tuning the reactive sites in pressure-induced oligomerization or polymerization. In the present work, we performed in situ high-pressure Raman spectroscopy and angle dispersive X-ray diffraction (ADXRD) experiments to explore chemical reactions of cyanamide up to 21.7 GPa via in a diamond anvil cell (DAC). We also measured the Raman, NMR and UV absorption spectra to study the property and structure of recovered samples. The subsequent analysis of reaction kinetics from 4.7 to 11.8 GPa illustrated the dependence of the rate constant with pressure. For further understanding the reaction mechanism, we also discussed the relation between tuning pressure and the selectivity of reactive sites.

4


Page 4 of 36

Page 5 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Experimental Section Commercially available cyanamide crystal (purity>98%) was purchased from Alfa Aesar Co. without further purification before utilization. A set of symmetric diamond anvil cells with 500 µm diamond anvils was used to load the sample. In the center of a pre-indented 40-µm-thick T301 stainless steel gasket, a 140-µm-diameter hole was drilled to serve as a sample chamber. Considering the sample is sensitive to air and water, a glove box (nitrogen atmosphere) was used for the process of the sample crushing and loading. Since it easily reacts with most PTM (pressure transmitting medium), no pressure medium was used in the experiment. The standard ruby fluorescence method18 was applied to measure the pressure in the diamond anvil cell and the ruby fluorescence peaks kept sharp clearly identified during all the process of compression with the highest pressure of 21.7 GPa. High-pressure Raman spectra of cyanamide were recorded using ARC-SP 2500 spectrograph (Princeton Instruments) equipped with the liquid nitrogen cooled charge coupled detector (PyLoN: 100B). The 532 nm wavelength laser from the diode pumped solid state (DPSS) with power of 0.5 mW was utilized to excite the sample. Raman measurements with 671 nm wavelength laser (2 mW) and 785 nm wavelength laser (5 mW) were performed by a microRaman system assembled around a spectrometer (iHR 550, Horiba Jobin Yvon) with a thermoelectrically cooled CCD (Synapse, Horiba Jobin Yvon). Each spectrum consumed 30 s as integration time. The pressure in the sample holder was measured after equilibrating DAC at each pressure for 5 min. All the Raman data were collected from the same region of the sample in each experiment. The absorption spectra measurements were carried out with the Ocean Optics QE65000 spectrometer. Samples for

13

C and 1H NMR experiments were prepared by

multi-anvil system with the standard COMPRES 10/5 sample assembly consisting of a 10-mm

5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

spinel (MgAl2O4) + MgO octahedron and were kept at 15 GPa for 1 hour.

Page 6 of 36

13

C and 1H NMR

spectra were recorded on a Bruker-400 (400 MHz) spectrometer using DMSO-d6 as solvent. 13C and 1H NMR chemical shifts were referenced versus DMSO-d6.19 Chemical shifts are reported in parts per million (ppm) and coupling constants are reported in hertz (Hz). Angle-dispersive XRD experiments were carried out at the 4W2 beam line of Beijing Synchrotron Radiation Facility (BSRF), and partial data were collected at Shanghai Synchrotron Radiation Facility (SSRF). An image plate detector (MAR-345) was used to collect Bragg diffraction rings. The FIT2D software was used for the two-dimensional XRD images in further analysis20, yielding one-dimensional intensity versus diffraction angle 2θ patterns. The monochromatic X-ray 0.6199 Å beam in size of 20 × 30 µm2 was utilized for data collection. The average acquisition time was 600 s. A CeO2 standard was used to calibrate the sample to detector distance and geometric parameters. Further analysis was performed with commercial Materials Studio to gain accurate lattice parameters. All experiments were carried out at room temperature.

6


Page 7 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Results of in situ High-Pressure Experiments Raman spectra ranges of 50 to 1300, 1400 to 2500 and 2750 to 3500 cm−1 at selected pressures are presented in Figure 2. And the pressure-induced frequency shifts of these modes are shown in Figure S1. In addition, the Raman modes of cyanamide in Table S1 are assigned based on information from literatures.21-23 During compression, a new broad peak from 1400 to 1700 cm−1 (centered at about 1580 cm-1) emerged at 13.3 GPa (Figure 2b). According to reported assignment, this peak represents the vibration of C=N and indicates pressure-induced chemical transformation of C≡N bonds into conjugated C=N double bonds.24-28 As a common phenomenon, the intensity of this new peak is weak at the beginning of the reaction.24,27 Two new peaks marked by the arrows shown in Figure 2a represent the vibrations of the skeleton and the new band at 1018 cm−1 represents the modes of the stretching vibration of C−C bonds.25-28 Meanwhile the N−C≡N out-of-plane bending band at 435 cm−1, N−C≡N sym-stretching band at 1140 cm−1, NH2 scissor bending band at 1550 cm−1 and N−C≡N anti-sym-stretching band at 2250 cm−1 broadened and weakened at 13.3 GPa, and eventually vanished at about 18.1 GPa. A new band of disordered cyano-groups appeared on the left of the original N−C≡N anti-symstretching band. This band at 2205 cm−1 (such as C≡N groups in hydrogen cyanide)29 suggests that a small number of C≡N groups survive the reaction. All of these significant changes indicate that the number of cyano-groups is reduced due to the occurrence of the chemical reaction above 13.3 GPa. The Raman modes of N−H vibrations ranging from 2800 cm−1 to 3600 cm−1 exhibited red-shift with no abrupt change up to 11.3 GPa. This result can be explained by the general rule that elevating pressure decreases the N−H stretching frequencies of weak and medium strength N−H···N hydrogen bonds.30 When the H···N distance was reduced by compression, the electrostatic attraction between H···N increased, thereby lengthening the N−H bonds and

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

reducing their stretching frequency. Compared with materials without hydrogen bonds (such as chemical transition of sodium cyanide at 25 GPa), the reaction of cyanamide has been shown to occur at a lower pressure.24 Additionally, the ordinary blue-shifts of the external Raman modes below 13.3 GPa in Figure 2a were caused by the reduction of intermolecular distances induced by increasing pressure. A new broad band (marked by dashed lines in Figure 2a) emerged as the background of the external Raman modes at 13.3 GPa. This phenomenon indicates the occurrence of the reaction almost broke original crystal state of cyanamide. This change is not complete at the beginning of the reaction and the Raman spectroscopy could detect the vibration of residual cyanamide molecules at 13.3 GPa. Subsequently, all the external modes faded into this broad background, which means that the reaction tended to be complete at about 18.1 GPa. These results provide evidence of the chemical reaction in cyanamide as well. To confirm the pressure-induced reaction of cyanamide, in situ high-pressure ADXRD experiment was also performed. The evolution of the representative XRD patterns up to 18.2 GPa is depicted in Figure 3. When the pressure reached 13 GPa, all peaks receded and a broad background appeared. These features indicate a change from the original crystalline state to a disordered state with a loss of long-range order.24,31 This abrupt change is consistent with the discontinuity in the Raman spectra at about 13.3 GPa in Figure 2. The pressure dependence of the unit cell parameters and the volume of cyanamide below 12 GPa are illustrated in Figure 4. The compression of the initial structure is anisotropic, and the c-axis is less compressible than the a-axis and b-axis, which indicates that the functional groups (C≡N groups) aggregate along the a-axis or b-axis as the most likely orientation of reaction. In addition, ADXRD patterns of the recovered samples provide decisive evidence for the non-reversible transitions of cyanamide under high pressure.

8


Page 8 of 36

Page 9 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Recovered Samples Based on the Raman spectra of pristine cyanamide and quenched samples in Figure 5, two broad peaks centred at around 1347 and 1550 cm−1 were observed, which are similar to the diamond D and graphite G bands of disordered graphite.24 Additionally, no signs of common N−N Raman stretching modes (such like hydrazine)32 were observed. Considering the thermal instability of the N−N bonds, N−N bonds have not formed in the products.33,34 All of the new features are maintained in the recovered sample, which also indicates that the chemical reaction is irreversible. Larger scale of pressure treated samples for

13

C and 1H NMR experiments were

prepared by multi-anvil system in further study of the reaction. Raman spectra in Figure 5 indicate these samples are the same as those prepared by DAC.

13

C NMR spectra of samples

both before and after pressing to 15 GPa are shown in Figure 6. Several new peaks in region from 158 to 168 ppm indicating the formation of C=N groups in high-pressure products and the original sharp peak at 116.71 ppm corresponding to the monomer (cyanamide with C≡N groups) barely existed. The results in 1H NMR spectra of high-pressure products versus the monomer (Figure S2) also indicate that the reaction occurred with significant changes in the chemical environment around H of NH2 groups. And it can be found the products contain complex structures by both 13C and 1H NMR spectra. The weak peak at 118.58 ppm in Figure 6 indicates very few functional groups (C≡N) to survive during the reaction. The products cannot be well dissolved in several deuterated organic solvents (such as Acetone-d6 and CDCl3), but can be dissolved in DMSO-d6, which indicates that the products are oligomers. Additionally, the UV spectra can reflect conjugated structure in reaction products. In Figure S5, the broad absorption peak of product recovered from 21 GPa shifted to higher wavelength than that of cyanamide at 0 GPa, and a new peak emerged at about 420 nm. These results indicate that systems of conjugated

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 36

double bonds were formed35,36 Therefore, all the observed spectral changes indicate the pressureinduced oligomerization in cyanamide is irreversible, and the products have a complex conjugated structure. Reaction Kinetics To understand the influence of pressure on the reaction rate, we studied the reaction kinetics by monitoring the change of intensity of the C≡N band at 2250 cm−1 under different pressures with 532 nm wavelength laser. To check the laser effect on the reaction, we have also used 785 nm and 671 nm wavelength laser to measure the evolution of Raman spectroscopy at 6.6 GPa, 7.9 GPa, 9.0 GPa, 10.5 GPa, and have found the results are basically the same as those under 532 nm wavelength laser (Figure S6−8). Samples of cyanamide under exposure of 532 nm wavelength laser for over 6 hours at 1.0 GPa were unchanged after a week and the same irradiation condition did not change the reaction process at 10.5 GPa (Figure S9). All these phenomena suggest that pressure acted as the main inducement in the oligomerization of cyanamide, and the short exposure under 532 nm wavelength laser with power of 0.5 mW had no effect on the reaction. Meanwhile, the samples prepared by multi-anvil system were without laser irradiation and the NMR results also confirmed that the reaction was only induced by pressure (Figure 6). The Avrami model, describing the growth of a crystal from a liquid phase, was extended to the analysis of solid-state reactions in recent years.1,14 The time evolution of normalized Raman area of the C≡N stretching modes were fitted by eq 1 according to the Avrami model. k is the reaction rate, n is a parameter related to the dimensionality of the growth, At, A0 and A∞ are the parameters of cyanamide at time t, at the beginning and at the equilibrium respectively.14 n

At = A∞ + ( A0 − A∞ )e −[ k ( t −t0 )]

10

(1)


Page 11 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The reaction kinetics was followed by the Raman intensity decrease of the C≡N band at 2250 cm-1. Examples of the evolution about the normalized area of the C≡N Raman band well fitted as a function of time at constant pressure are reported in Figure S10. The n values are all less than 1 and the average is 0.75, which implies a one-dimensional growth at the beginning of the reaction.1,14 Meanwhile different k values in Table S2 indicate that elevating pressure increased the reaction rate. According to the transition state theory, the dependence of the rate constant k versus pressure at constant temperature is given by eq 2. ∆ ≠V  ∂ ln k  = −   RT  ∂P T

(2)

The activation volume of the reaction (∆≠V) was determined by the relationship between the reaction rate and pressure. The evolution of ln k as a nonlinear function of pressure can be fitted in a parabolic law.14,15 According to the quadratic dependence of the ln k versus pressure given by eq3 with a = −9.74, b = 1.00, and c= −0.02 in the Figure 7, the activation volume values at different pressures were obtained by eq 4.14,15 ln k = a + bP + cP 2

(3)

∆ ≠V = − ( b + 2cP ) RT

(4)

The values of activation volume from 4.7 GPa (−2.01 cm3 mol−1) to 11.8 GPa (−1.31 cm3 mol−1) at selected pressures are shown in Table S2. The changes of activation volume indicated the reaction was accelerated by elevating pressure.

Discussion According to reported literatures, the associative process about formation of covalent bonds has a negative contribution to the activation volume and the dissociative process about breaking of covalent bonds has a positive contribution to the activation volume.1,7,14,15 The negative values

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 36

of activation volume indicate that the formation of new bonds depends on rearranging the cyanamide molecules and decreasing the volume of the system. The observed increase of the ∆≠V values with pressure is attributed to the enhanced steric hindrance of the system. The small value of ∆≠V can be interpreted as the rise of competitive effect of the positive contribution (diffusion process) and the negative contribution (the formation of new bonds) to the activation volume. Considering the kinetics study with the transition state theory, high pressure reduced the distance among functional groups, increased the density of the initial samples, lowered the activation free energy and accelerated the reaction. Meanwhile the steric factors also affected the reaction mechanism. The increase of the activation volume indicated the system became denser by elevating pressure. The enhanced steric hindrance of the system changed proximity of reactive sites. Selected Raman spectra of recovered cyanamide at different pressures are shown in Figure 8, and major Raman modes are assigned based on literature.25-28 When the samples were subjected to a higher pressure, the relative intensity of the C−C stretching band at 980 cm−1 gradually strengthened and C−N stretching band at 930 cm−1 gradually weakened. Additionally, there was an intensity exchange among characteristic bands of the C−C and C−N segments above 7.9 GPa. These results indicate that, from 4.5 GPa to 11.8 GPa, the C−C and C−N bonds coexisted in the products and the formation of C−N bonds occupied the main part of the reactions below 7.9 GPa, because the close C···N distance (Table S3) made C and N atoms of adjacent C≡N groups act as the most likely reactive sites. When the value of pressure was elevated, the amount of C−C bonds increased and the amount of C−N bonds gradually decreased in the products. Meanwhile C···C of adjacent C≡N groups has a more compressible distance and it has a tendency for these C atoms to become the closest reactive sites above 7.9 GPa (Table S3). It can be explained by the

12


Page 13 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


following analysis: the reactive sites of C≡N groups were changed by elevating pressure, thereby making it more likely to form C−C bonds in the oligomerization process. These phenomena indicate that elevating pressure tuned the reactive sites and selected the formation of new bonds.

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 36

Conclusion In summary, we have performed in situ high-pressure studies of cyanamide using Raman spectroscopy and synchrotron X-ray diffraction. The abrupt changes in the Raman spectra provided convincing evidence for the occurrence of oligomerization at about 13.3 GPa. In addition, the chemical reaction broke the original arrangement of hydrogen bonds and changed the crystal of cyanamide into a disordered state, which is consistent with the discontinuity of ADXRD spectra under pressure. Moreover, the solubility of the high-pressure products confirmed the recovered samples were oligomers. The Raman, NMR and UV absorption spectra of the high-pressure products illustrated that C=N bonds formed exactly and the oligomerization was irreversible. The subsequent discussions of reaction kinetics indicated that elevating pressure changed the activation volume and increased the reaction rate. Meanwhile, high pressure selected C···C of adjacent C≡N groups as reactive sites and an increase in the amount of C−C bonds was observed as the pressure increased. We believe that pressure is an important factor in tuning reactive sites in oligomerization and even other chemical reactions in the future.

14


Page 15 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Crystal structure of cyanamide at ambient conditions: (a) the hydrogen-bonds system view along the b-axis; (b) Unit cell of cyanamide. The hydrogen bonds are denoted by dashed lines.

15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 36

Figure 2. Raman spectra of cyanamide at high pressures: (a) 50−1300 cm−1; (b) 1400−2500 cm−1; (c) 2750−3500 cm−1. (ν, stretching; γ, out-of-plane bending; δ, in-plane bending; s, symmetric; as, asymmetric) The inset in Figure 2b is the Raman spectra from 1400 to 2000 cm−1 at 13.3 GPa.

16


Page 17 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Representative angle-dispersive X-ray diffraction patterns of cyanamide at different pressures and after pressure release. The wavelength for data collection is 0.6199 Å.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. Unit cell volume of cyanamide with respect to pressure, (Inset) Anisotropic pressure response of the crystal lattices.

18


Page 18 of 36

Page 19 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. The Raman spectra of recovered samples prepared by DAC and muti-anvil system compared with cyanamide at ambient condition in the region from 50 to 3600 cm−1.

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. 13C NMR spectrums of high-pressure products prepared from multi-anvil system and monomer in DMSO-d6 (100 MHz, DMSO-d6).

20


Page 20 of 36

Page 21 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Quadratic fit of the ln k as a function of pressure at ambient temperature (298 K).

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8. Selected Raman spectra of recovered cyanamide from reactions at different pressures.

22


Page 22 of 36

Page 23 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Supporting Information Experimental detail information about Raman spectroscopy, 13C NMR, 1H NMR, synchrotron X-ray diffraction, UV-Vis absorption spectra cited in manuscript. This material is available free of charge via the Internet at http://pubs.acs.org.

Corresponding Author *E−mail: [email protected]. *E−mail: [email protected]. *E−mail: [email protected]

Notes The authors declare no competing financial interests.

Acknowledgments This work is supported by NSFC (Nos. 91227202, and 11204101), RFDP (No. 20120061130006), Changbai Mountain Scholars Program (No. 2013007), National Basic Research Program of China (No. 2011CB808200), China Postdoctoral Science Foundation (No. 2012M511327). Angle-dispersive XRD measurement was performed at 4W2 beamline, Beijing Synchrotron Radiation Facility (BSRF) which is supported by Chinese Academy of Sciences (No. KJCX2-SW-N20, KJCX2-SW-N03). Portions of this work were performed at the 15U1 at the Shanghai Synchrotron Radiation Facility (SSRF). We thank Mr. Lingwei (Willian) Kong (Pembroke Pines Charter High School, Miami) for English polish.

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 36

References (1) Schettino, V.; Bini, R.; Ceppatelli, M.; Ciabini, L.; Citroni, M. Chemical Reactions at Very High Pressure. Adv. Chem. Phys. 2005, 131, 105-242. (2) Starkweather, H. W. Polymerization under High Pressure. J. Am. Chem. Soc. 1934, 56, 1870-1874. (3) Bini, R. Laser-Assisted High-Pressure Chemical Reactions. Acc. Chem. Res. 2004, 37, 95-101. (4) Murli, C.; Song, Y. Pressure-Induced Polymerization of Acrylic Acid: a Raman Spectroscopic Study. J. Phys. Chem. B 2010, 114, 9744-9750. (5) Horvath-Bordon, E.; Riedel, R.; McMillan, P. F.; Kroll, P.; Miehe, G.; van Aken, P. A.; Zerr, A.; Hoppe, P.; Shebanova, O.; McLaren, I.; Lauterbach, S.; Kroke, E.; Boehler, R. HighPressure Synthesis of Crystalline Carbon Nitride Imide, C2N2(NH). Angew. Chem. Int. Ed. 2007, 46, 1476-1480. (6) Grochala, W.; Hoffmann, R.; Feng, J.; Ashcroft, N. W. The Chemical Imagination at Work in Very Tight Places. Angew. Chem. Int. Ed. 2007, 46, 3620-3642. (7) Yoo, C. S.; Nicol, M. Kinetics of a Pressure-Induced Polymerization Reaction of Cyanogen. J. Chem. Phys. 1986, 90, 6732-6736. (8) Ciabini, L.; Santoro, M.; Bini, R.; Schettino, V. High Pressure Photoinduced Ring Opening of Benzene. Phys. Rev. Lett. 2002, 88, 085505. (9) Santoro, M.; Gorelli, F. A.; Bini, R.; Haines, J.; Van Der Lee, A. High-Pressure Synthesis of a Polyethylene/Zeolite Nano-Composite Material. Nat. Commun. 2013, 4, 1557. (10) Citroni, M.; Ceppatelli, M.; Bini, R.; Schettino, V. Laser-Induced Selectivity for Dimerization versus Polymerization of Butadiene Under Pressure. Science 2002, 295, 20582060. (11) Fitzgibbons, T. C.; Guthrie, M.; Xu, E.; Crespi, V. H.; Davidowski, S. K.; Cody, G. D.; Alem, N.; Badding, J. V. Benzene-Derived Carbon Nanothreads. Nat. Mater. 2015, 14, 43-47. (12) Ni, B.; Wang, K.; Yan, Q.; Chen, H.; Ma, Y.; Zou, B. Pressure Accelerated 1,3-Dipolar Cycloaddition of Azide and Alkyne Groups in Crystals. Chem. Commun. 2013, 49, 1013010132. (13) Wilhelm, C.; Boyd, S. A.; Chawda, S.; Fowler, F. W.; Goroff, N. S.; Halada, G. P.; Grey, C. P.; Lauher, J. W.; Luo, L.; Martin, C. D.; Parise, J. B.; Tarabrella, C.; Webb, J. A. PressureInduced Polymerization of Diiodobutadiyne in Assembled Cocrystals. J. Am. Chem. Soc. 2008, 130, 4415-4420. (14) Citroni, M.; Ceppatelli, M.; Bini, R.; Schettino, V. High-Pressure Reactivity of Propene. J. Chem. Phys. 2005, 123, 194510.

24


Page 25 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Nobrega, M. M.; Ceppatelli, M.; Temperini, M. L.; Bini, R. Pressure-Induced Reactivity in the Emeraldine Salt and Base Forms of Polyaniline Probed by FTIR and Raman. J. Phys. Chem. C 2014, 118, 27559-27566. (16) Hetherington, H.; Braham, J. The Hydrolysis and Polymerization of Cyanamide. J. Am. Chem. Soc. 1923, 45, 824-829. (17) Denner, L.; Luger, P.; Buschmann, J. X-Ray Structure of Cyanamide at 108 K. Acta Crystallogr., Sect. C 1988, 44, 1979-1981. (18) Mao, H. K.; Bell, P. M.; Shaner, J. W.; Steinberg, D. J. Specific Volume Measurements of Cu, Mo, Pd, and Ag and Calibration of the Ruby R1 Fluorescence Pressure Gauge from 0.06 to 1 Mbar. J. Appl. Phys. 1978, 49, 3276−3283. (19) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62, 7512-7515. (20) Hammersley, A.; Svensson, S.; Hanfland, M.; Fitch, A.; Hausermann, D. TwoDimensional Detector Software: From Real Detector to Idealised Image or Two-Theta Scan. High Pressure Res. 1996, 14, 235−248. (21) Durig, J.; Walker, M.; Baglin, F. Lattice Vibrations of Molecular Crystals. II. Cyanamide and Cyanamide-d2. J. Chem. Phys. 2003, 48, 4675-4682. (22) Fletcher, W. H.; Brown, F. B. Vibrational Spectra and the Inversion Phenomenon in Cyanamide and Deuterated Cyanamide. J. Chem. Phys. 2004, 39, 2478-2490. (23) Wagner Jr, G.; Wagner, E. Vibrational Spectra and Structure of Monomeric Cyanamide and Deuterio-Cyanamide. J. Phys. Chem. 1960, 64, 1480-1485. (24) Chen, J.; Yoo, C. S. Physical and Chemical Transformations of Sodium Cyanide at High Pressures. J. Chem. Phys. 2009, 131, 144507. (25) Yoo, C. S.; Nicol, M. Chemcal and Phase Transformations of Cyanogen at High Pressures. J. Phys. Chem. 1986, 90, 6726-6731. (26) Tomasino, D.; Chen, J.; Kim, M.; Yoo, C. S. Pressure-Induced Phase Transition and Polymerization of Tetracyanoethylene (TCNE). J. Chem. Phys. 2013, 138, 094506. (27) Li, K.; Zheng, H.; Ivanov, I. N.; Guthrie, M.; Xiao, Y.; Yang, W.; Tulk, C. A.; Zhao, Y.; Mao, H. K. K3Fe(CN)6: Pressure-Induced Polymerization and Enhanced Conductivity. J. Phys. Chem. C 2013, 117, 24174-24180. (28) Simons, T.; Howlett, P.; Torriero, A.; MacFarlane, D.; Forsyth, M. Electrochemical, Transport, and Spectroscopic Properties of 1-Ethyl-3-Methylimidazolium Ionic Liquid Electrolytes Containing Zinc Dicyanamide. J. Phys. Chem. C 2013, 117, 2662-2669. (29) Aoki, K.; Baer, B.; Cynn, H.; Nicol, M. High-Pressure Raman Study of One-Dimensional Crystals of the Very Polar Molecule Hydrogen Cyanide. Phys .Rev. B 1990, 42, 4298-4303.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 36

(30) Hamann, S. D.; Linton, M. The Influence of Pressure on the Infrared Spectra of Hydrogen-Bonded Solids. Ⅲ Compounds with N−H···X Bonds. Aust. J. Chem. 1976, 29, 16411647. (31) Goncharov, A. F.; Manaa, M. R.; Zaug, J. M.; Gee, R. H.; Fried, L. E.; Montgomery, W. B. Polymerization of Formic Acid under High Pressure. Phys. Rev. Lett. 2005, 94, 065505. (32) Durig, J.; Bush, S.; Mercer, E. Vibrational Spectrum of Hydrazine-d4 and a Raman Study of Hydrogen Bonding in Hydrazine. J. Chem. Phys. 2004, 44, 4238-4247. (33) Pottie, R.; Lossing, F. Free Radicals by Mass Spectrometry. XXV. Ionization Potentials of Cyanoalkyl Radicals. J. Am. Chem. Soc. 1961, 83, 4737-4739. (34) Kliss, R. M.; Matthews, C. N. Hydrogen Cyanide Dimer and Chemical Evelution. Proc. Natl. Acad. Sci. USA 1962, 48, 1300-1306. (35) Ogawa, K.; Mino, N.; Tamura, H.; Hatada, M. Polymerization of a Chemically Adsorbed Monolayer of an Acetylene Derivative. Langmuir 1990, 6, 1807-1809. (36) Subramanyam, S.; Blumstein, A. Conjugated Ionic Polyacetylenes. 3. Polymerization of Ethynylpyridinium Salts. Macromolecules 1991, 24, 2668-2674.

26


Page 27 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents Graph

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 36

Crystal structure of cyanamide at ambient conditions: (a) the hydrogen-bonds system view along the b-axis; (b) Unit cell of cyanamide. The hydrogen bonds are denoted by dashed lines. 76x35mm (300 x 300 DPI)


Page 29 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Raman spectra of cyanamide at high pressures: (a) 50−1300 cm−1; (b) 1400−2500 cm−1; (c) 2750−3500 cm−1. (ν, stretching; γ, out-of-plane bending; δ, in-plane bending; s, symmetric; as, asymmetric) The inset in Figure 2b is the Raman spectra from 1400 to 2000 cm−1 at 13.3 GPa. 152x119mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Representative angle-dispersive X-ray diffraction patterns of cyanamide at different pressures and after pressure release. The wavelength for data collection is 0.6199 Å. 76x114mm (300 x 300 DPI)


Page 30 of 36

Page 31 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Unit cell volume of cyanamide with respect to pressure, (Inset) Anisotropic pressure response of the crystal lattices. 76x76mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Raman spectra of recovered samples prepared by DAC and muti-anvil system compared with cyanamide at ambient condition in the region from 50 to 3600 cm−1. 76x41mm (300 x 300 DPI)


Page 32 of 36

Page 33 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13C NMR spectrums of high-pressure products prepared from multi-anvil system and monomer in DMSO-d6 (100 MHz, DMSO-d6). 76x61mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Quadratic fit of the ln k as a function of pressure at ambient temperature (298 K). 76x101mm (300 x 300 DPI)


Page 34 of 36

Page 35 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Selected Raman spectra of recovered cyanamide from reactions at different pressures. 50x88mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents Graph 50x39mm (300 x 300 DPI)


Page 36 of 36

Selected Reactive Sites Tuned by High Pressure ... - ACS Publications

Recommend Documents